The quantity of oil you mention strikes me as more than just weepage, such as the valve cover gasket or oil pan. A gasket may be weeping, but not like what you're saying. The gaskets should still be occasionally checked for signs of weeping, especially at the back of the engine where leaks are out of sight. For the valve cover gasket, installers are advised to put RTV gasket seal at the corners of the cam journals, especially with the thicker gaskets. Many don't, so if you find leaks there, that's why. The valve cover nuts may occasionally need re-tightening, also the oil pan. A moderate light torque is called for, evenly around the gasket. For the valve cover, 10-11 ft.lbs is called for. I'll often go 12-13 for an older gasket that's weeping. The old stamped steel valve covers were to be cross tightened, yours is cast aluminum.

A soft engine mount means there's been long-term exposure to accumulations of oil or oily grunge. For the passenger side mount, often the main source of oil there is changing the oil filter and not cleaning up down at the cross member. Pack oil rags or paper towels down there prior to removing the filter, even crumpled newspaper. Once loosened, spin it off immediately with a rag/towel underneath to minimize oil down the block. Immediately tip it up so you can take your time extracting it around between the fender. Removing the preheat shroud on the manifold helps (highly recommended to leave the hose disconnected afterwards to help prevent cooking the expensive AMM when, not if, the airbox thermostatic plunger fails). Another option is puncturing the filter and letting it drain first. Afterwards, clean up the crossmember area of oily grunge, even crawling underneath to wipe inside the drain hole.

Fresh looking oil down below the filter can be spillage when filling, but the plug recesses often get the worst of it or else it goes down behind the timing cover. If it keeps coming back like you say,, suspect a loose oil filter, a mis-seated oil filter ring or a filter tightened with a wire caught behind it, like the oil pressure sensor wire. If it's clean oil, suspect this happened after a recent oil change.

If it's a recently purchased car, what are the odds the PO was in a rush to top it up or do a last minute oil change, got sloppy, didn't check their work, and didn't clean up? That would be my immediate guess based on what you've said about clean oil.

Other sources of significant continual oil leaks are a blown out, or partially blown out seals, either one of the three front engine seals o, possibly even the rear main seal, evidenced by oil collecting at the base of the timing cover or the trans bellhousing, almost always a sign of a poorly maintained PCV system.

In 240s without the rear distributor, a blown out half-moon plastic plug that lives below the valve cover at the rear cam area makes for a sudden loss of oil, often seen on the roadway, another sign of a poorly maintained PCV system. A retaining strap with holes can be placed behind it to keep it from blowing out. Threaded bolt holes in the block are already present. IPD used to sell a strap kit, but you can easily make it yourself.

Leakage at the oil sensor on the block can be evidenced by paper towel or visually after starting with a clean engine.

It's worth checking the belly pan when working on the engine, especially at the back. Oily grunge collecting at the back of the belly pan is common with old engines from weeping gaskets. Significant amounts of oil collecting there suggests spillage or a problem that needs investigating. You might even find the odd lost washer, nut, bolt or tool. The belly pan is there for a number of reasons. It prevents road spray from getting to the engine compartment, also splashes going through deep puddles and slush. It's also there for air flow. It forces air flow around the engine to help with cooling. In combination with the front bumper air dam, it also reduce air flow under the car and at high speed can reduce drag by forcing air over the car, also helping it to hug the road. The belly pans often get damage and should occasionally be repaired or replaced. Aluminum belly pans are available in the aftermarket.

BTW, oil vapour residue collecting around the filler cap is common. You need to replace the rubber oil ring, not the entire cap. Every other oil change is a good guideline. I always keep a few on hand, often adding them to an order to save on shipping. At each oil change, lift up the rubber ring and if it's not flexible it needs replacing. If it's dried it will be stiff and easily break, a sign it's overdue. If the cap doesn't feel snug while being tightened then the ring is dried out and needs replacing. The tangs on the cao rarely if ever need to be tweaked, except maybe those used with the old stamped steel valve covers, not so much the newer cast aluminum covers.

Yes, the V90s are new, if you consider 25 years new. The early series of 1997-1998 V90s were RWD, basically a re-badged 960. After a gap in production, the 90 series came back in 2016 as a long wheelbase FWD, still produced, but its days are numbered. The XC90 was popular as an SUV.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Hi,

I second the thought about the oil pressure switch as it only takes the tiniest crack or just a loosening of the crimp holding the dome of the switch to create a leak from some direct pressures of pump flow.

A valve cover gasket has seepages downward into the spark plug wells and maybe gets farther down the iron block. These have with lots of dirt and gunk buildup.
Clean oil is a clue that it is more than a seepage.
The rear plug mentioned can even manage to leak oil down the back side of the block, run around the oil pan lip, to make you think it’s a pan gasket or even a rear Main seal.

A front cam seal seeps onto the water pumps housing.
If and when the front crankshaft seal leaks the wiring harness, under the engine there, gets very nasty.
If you find that kind of stuff please inspect the timing belt as oil can be very detrimental to them.

If your rubber mounts got soft it’s either the switch or some very careless oil filter changing.
Fresh hot detergent oil is designed to do just that, dissolve and suspend.
I believe synthetic rubbers are made black from carbon pigments.

Was the belly pan holding any appreciable amounts of that engine oil?
This socket and wrench catching invention, or a gravel shield named by from some vendors, is a good place to keep in your sites on with numerous observations.
Oil filter spillage runs pretty much gets to go everywhere and will soak the cross member along with the plastic pan lip.

Getting things back to fresh metal is a mandatory first step.
The worse offender will have the thinner and cleanest oil residue trails and thicker dark ones that resist removal.
The oldest are layered with dirt that’s a convenient bonding or building agent.

I’m sure glad you are pawing all over this car as the payback of some tremendous smiling is ahead!

Phil

The oil pressure switch is near the front of the motor in line with the filter. I suggest you wash the motor so you can really see what's going on.

If you are lucky, it is the valve cover or more likely the oil cap gasket. Clean the engine so you can check there and some other usual suspects…:) Once clean, check the camshaft and crankshaft seals in the front. Another leak spot is the rear of the head where a plug is installed (some 7 and 940’s have distributers there). Plugs used there in 240’s instead to fill hole.

Yes, the breather system (including the flame trap, breather box and related hoses) are known for clogs and subsequent excessive crankcase pressure. If you don’t know the car’s history, buy at a minimum a new flame trap and its hoses. The hose that runs from the intake manifold to the flame trap is a common culprit for clogs (my 90 240’s problem that took forever to find!). As is the hose from the flame trap to the breather box. If you don’t fix excessive crankcase pressure it will simply blow through any new seals again.

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Will I buy another Volvo??? We'll see....