Your Volvo doesn't really have a PCV valve like most other engines. Rather, it is more of a box with a fixed orifice that vents the crankcase.
Here is a description of how this crankcase ventilation system works:
Crankcase gases are removed from the cylinder block (and cylinder head to an extent) to an oil trap (1) where oil is separated from the crankcase gases and returned to the oil sump. The hose to the cylinder head equalizes differences in pressure between the upper and lower parts of the engine.
When there is little load on the engine or when it is idling there is no under-pressure in the fresh air hose and only a small quantity of crankcase gases are formed. Because of this a vacuum hose (7), to lead crankcase gases directly to the intake manifold at low loads, goes from the heating nipple to a calibrated intake downstream of the throttle.
The heating nipple is calibrated to provide a controlled flow of crankcase gases. Power to the PTC type nipple is supplied by the engine management system main relay and prevents water vapor in the crankcase gases from freezing in the fresh air intake hose at low temperatures.
The PTC nipple temperature stabilizes at approximately 80°C (176°F) as soon as the engine is started.
If you engine is leaking oil, it is likely because the seals are old and have shrunk. I would recommend changing the oil and using a "high mileage" oil designed for cars with over 75,000 miles on the engine. Valvoline is a good brand. The oil contains additives to help older seals swell and regain some elasticity. That should help slow down or stop the oil leaks.
As for a "cheap" service manual, try ebay.