Sounds like you got a nice car. Too bad about the quirks.

1. Find another mechanic. First: The overdrive relay can be removed, re-soldered and reinstalled in an hour and at no cost. Second: The transmissions usually go 200K without a problem if they have been at least minimally maintained. Third: The PCV system os soooo obvious that forgetting is is merely a money-maker for the mechanic. Also, servicing the PCV system is a DIY job.

2. The solenoid is a DIY job. Greasy but cheap. But first, check it out. It is under the car on the driver side. You can test with a test light to see if it's getting current. Or, with the engine stopped, lean out and listen for a click when you push the shifter button.

3. Rear main seal. When the PCV valve* is clogged, natural pressure build up in the crankcase has nowhere else to go, so it blows past one or more seals. The front and rear main seals, intermediate shaft seal or cam shaft seal. Your rear main seal was likely the weak point, no logic. If the PCV system is really running right, the leak will practically disappear. BTDT.

* The Volvo B230F engine doesn't have a PCV valve. The system uses a flame trap, oil separator box, and vacuum hoses, all of which can clog up. Is that mechanic Volvo trained?

Good Luck,

Bob

:>)