Here is the Volvo Maint schedule:

https://www.customers.volvocars.com/owners/docs/1998/1998_maintenance/1998_all_maintenance.html

Here's how I found it:
http://www.volvocars.com/us/tools/OwnersInfo/Pages/VolvoOwners.aspx

Please note the recommendation to flush the brake fluid every two years, but only on owner's request. Do a complete fluid change and bleed your brakes.

I would add transmission fluid flush to that schedule.

A power steering system flush is a great way to add some service life to that system.

Coolant flush and thermostat change helps keep your engine internals/heater core/water pump going strong. The coolant should probably be changed every 5 years or so, and the thermostat should probably be changed every time you open that system up. Be sure to get an OEM thermostat.
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1998 V70 AWD Turbo 190k+

The rear cam seal leaks because the crankcase pressure is too high. The crankcase pressure is too high because your PCV system is clogged somewhere.

I would first check the vacuum line that goes down to the air intake line just before the turbo. Look down, pull off the line and see if the PTC nipple is clogged. Clean it gently and throughly. If this is the case, your oil leak might stop.

If you let the oil leak too long, it will get worse and coat the cam position sensor and your car will no longer run. A new CPS is not cheap. A new cam seal is cheap and easy to replace.

Klaus
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Common sense trumps a PhD