http://www.brickboard.com/FAQ/700-900/BuyingUsed7xx.htm

I just noticed this link within the RWD section here is the text. I think this list is fairly comprehensive of all of the big ticket items that can go wrong, but I think it's a disservice to imply that all 850's are lemons and suffer from the following problems:



Replacing Your 740/940 With an 850/70. [Query] My pristine 745 was totaled. I'm considering replacing it with an 850. Anything to watch for?

[Response] My 850 was an absolute lemon. But rather than bore you with details, here are the the most common 850/70 problems:

Rear Main Seals; costs about $1000 to repair (10-12 hrs labor): these are unreliable on all five cylinder engine cars. Clean the flame trap!
AC evaporator unit; costs about $1000 to repair
Auto transmission PNP switches failing
Auto transmission clutch failure and fluid overheating in earlier 850s: consider using synthetic and flushing regularly
Tie rod ends and ball joints fail at 50-70k miles
Heater fans
ABS control module failures(certain years); also affects traction control systems. These units can be rebuilt with repaired electronics.
Check engine and Service Soon lights seem to always come on and require a special reset device
Most use quite a bit of oil between changes
Also known for defective seat heaters, sunroof shades falling out of the tracks, peeling door panels, peeling moldings on roof, losing the rubber molding above the windshield, squeeks and rattles, noisy suspensions.
Make sure the timing belt has been replaced recently; if this snaps it ruins the engine. It is very expensive to have the belt replaced.
The 850's are more labor intensive than the 2/7/9 series and are more maintenance intensive, in most cases.

Moral: Keep your RWD Volvo going as long as you can.