I would STRONGLY encourage you to remove and clean the Breather Box (aka Oil Trap, Oil Seperator). Once I have it off the car, I spend at least 5 to 10 minutes of reaming out the vapor exhaust port and the oil return port. Then there's another 5 to 10 minutes of smacking the box with a screwdriver handle quite forcefully in order to break up the large chunks of dried oil inside it. -add in another 2 minutes of violently shaking it to get all the chunks out, and I'm done. I don't clean with throttle body or carb cleaner until I've got 95% of the soild matter removed (by shaking) as the carb cleaner will soften the dried oil chunks and cause them to stuck inside. (really, I get almost everything out without using carb cleaner)

It seems like I'm preforming this operation about once a month now (as more and more of my friends acquire or trade Volvo 200/700/900 cars) and almost every newly acquired Volvo is leaking oil because of this problem. After an hour or so of cleaning, the crankcase pressure is aleviated and the oil leaks stop. This operation should only need to be performed about every 100,000 or 150,000 miles, so spending the extra time to get it as clean as possible pays off.

Budget yourself about two hours for the operation (if you've never done it before) and you should solve your high crankcase pressure problem. Be thorough about getting the solid debris out of the breather box, and spend as long as it takes to open up the vapor and oil return ports. From your symptoms, they're going to be plugged almost solid, and you'll be scraping the oil with a screwdriver for some time to get them as open as they should be. A lot of air needs to move through this device, and the more resistance it causes, the more greater the quantity of oil that will be pushed out of the engine seals.

When cleaning the crankcase vent tubes after the Breather Box (flame trap and associated plumbing), ream these out with large bladed screwdrivers to extract the solid material (burned/dried oil) and then clean them with carb or throttle body cleaner.

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I'd advise pulling the entire Crank Case Ventilation system and giving it a good cleaning. Remove the Flame Trap if you have one installed in the T-fitting of the PCV hose (as per a Volvo Technical Service Buletin), and ream out the dried and burt oil from the hoses with a screwdriver. Also, remove the Oil Trap Breather Box that's bolted to the engine block just below intake runners #3 and #4. It's held there by a pair of 12mm or 13mm bolts. It needs to come up for a full inch before coming sideways and out from under the intake manifold. This box gets dried/burned oil buildup in it just like the Flame Trap, but it takes about 150,000 miles or so before it starts to plug up solid. Ream out the 3 ports on it with a screwdriver, smack the sides gently with the screwdriver handle (to brake free the huge chunks from the inside), and then clean it with Throttle Body Cleaner. Reinstall it using a new o-ring seal (available from FCP via part number 949659). It only requires one seal, since the other port on the bottom fits snug to a rubber hose in the block that drains the oil back down to the bottom of the oil pan (do not attempt to remove this hose or you will have to remove the oil pan to re-install it).
After cleaning the Oil Trap and the PCV tubing, you should eliminate the oil leakage coming from the front cam-shaft seal. It may not be obvious, but if you have oil on your waterpump housing, -that's where it's coming from. The high crankcase pressures force the oil and oil vapors out through the easiest exit, which is supposed to be the Oil Trap (which functions to vent the vapors to the intake and return the oil back to the pan), but has now become the front camshaft seal and/or other oil seals on the engine.
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God bless,
Fitz Fitzgerald.
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'87 Blue 240 Wagon, 253k miles.