Here's some other links from the past year or so:
http://grassrootsmotorsports.com/forum/grm/learn-me-volvo-850s/38356/page1/
http://grassrootsmotorsports.com/forum/grm/learn-me-volvo-850/39356/page1/
They're great cars, the white block will go forever. I'm over 200K on my car, and I'd guess around 150K on it's engine. The turbo's can make gobs of power, and the auto trans is good to up to ~300 WHP, the manual (yes the manual used on the N/A cars) is good to well north of that, but you'll need a Quaife to make use of that kind of power.
Mine is a N/A '95 GLT, auto. It's easily the most reliable car I've ever owned. I've done just about all the usual maintenance, and then some, so if you've got any specific questions just ask. I did an engine swap on mine, out of necessity, but because I was dumb enough to overheat the thing. New-to-me lower mileage engine was cheaper than a reman head.
My car has the common N/A mods, and then some. It's not "fast" but has no problem keeping up with traffic. I've got it slightly lowered on Eibachs and Koni oranges. Am considering the IPD anti-swaybars... now I'm rambling.
Parts are really no harder to find than anything else we've got. I use online retailers mostly. IPDUSA.com FCPEuro.com are my primary, and I've gotten reman CV axles and what not from O'Reilly's, have bought an O2 sensor and ignition coil from Autozone, and they were in-stock setting on the shelf didn't have to order. I have also found that parts prices really aren't any worse either, as long as you aren't shopping at the dealer.
There's several large forums dedicated to these cars, and anything you want to know has been asked before. I usually recommend Matthewsvolvosite.com first, it's the most Noob friendly, and general maintenance oriented of the forums.
Klayfish, have you had the spark plug cover off? If there's a pool of oil under there, replace your oil filler cap gasket, that's about the most common place to loose the quantity of oil you're loosing. A clogged PCV would exacerbate the problem.