I removed the intake manifold to change out my knock sensors. Its fairly difficult but with these instructions and a Haynes manual, it can be done. Volvospeed was kind enough to add the procedure to the Bay 13 section

http://volvospeed.com/Repair/knock_sensor.pdf

I also have a 1998 V70 AWD wagon. You mentioned oil and turbo which caught my eye. Among my car's many repairs, the most recent was the Turbo Drain Seals being replaced. Despite always taking my car to the dealer for scheduled maintainces, etc, one day I was VERY low on oil. According to my invoice , the leaking turbo tube seal needed to be replaced. Don't know if that has anything to do with your problem, but thought I'd mention it.

Hi, had to renew the input maniford gasget one year ago in my 850-94 N/A with 200kkm. There are a couple of difficult bolts to get to, but otherwise easy diy job. Most of my time was spent to clean all around as you have easy access. I also would renew the rubber vacum elbows below the manifold. Since is my oil pan bottom clean and dry. Just take few hours and have it done. br Tapsa

There is a simple check to see if your PCV is really the problem: Replace the oil fill cap with a pressure gauge. If there is positive pressure while the engine is running, the PCV system may be your problem. If negative (i.e. vacuum), then you're probably still OK. Your local garage can check this quickly. For what it's worth, the service manual says to clean at 60k and 100k.

If you have to tackle this (or just decide to anyway), beware it is no small job! To get to the oil separator, the intake manifold has to come off, requiring removal of the fuel rail/injectors and the throttle body. Plus, some of the bolts on the manifold are difficult to get at. It would be a good time for your tune-up, though, because one of the PCV lines runs back to the firewall area, and it's much easier to change with the distributor cap and ignition wires out of the way.
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1998 S70 T5, 5-speed, 140k