My 1996:

1) Alternator
2) ABS Control Module (twice)
3) Rear Main Seal
4) Starter
5) Cooling Fan
6) Heater Blower Motor
7) Power Antenna
8) Thermostat
9) Brake Rotors a few times
10) Check engine and service light were on constantly


Upon selling, I had a small coolant leak, it needed a sunroof seal and some small misc. things. Mine was a total lemon and very expensive to repair. Worst car I ever owned. Lots of sqeaks and rattles and lots of suspension noise. Volvo service and coprorate customer support are the worst.
--
96 850 GLT 5-Speed- Sold due to astronomical repair costs.

I have had my 850 T-5 for 6 years now, and it has about 120K highway miles. The only problem ever was a passenger side front bearing. I have recently decided to sell only because I am simply ready for a new car. These are great cars and I just wish the prices had not gone up so much in the last few years.

1997 859 Wagon (N/A, AT), bought used three years ago with ~62K miles on the clock:

1. Air pump had to be replaced @ 75K miles;
2. O2 sensor (one week after the air pump);
3. A/C needed to be recharged one year after I bought the car (not the last year, though) - probably the evaporator issue...

I have owned a 97 850 wagon for a while, so far I have had the following
problems,

front brake caliper froze up
thermostat replaced
ball joints
control arm bushing
noise in the rear suspension
noise and knocks in the front suspension.

no to bad, I think the 97 is the best year for the 850,
I have done all the recomended maint. to date the car has
69,000 miles on it, next week the car goes in for a timing belt.
I like the car but it not the best performer at 165 hp, I reget
not buying a turbo 850.

saftey for my wife and kids was the main reason we bought the car

good luck

I think most people would prefer to purchase a used car from the original owner as you get a better history of how the car was driven and maintained. Make sure the owner has the service records and check the records for regular maintenance including regular oil changes, tranmission fluid changes, etc. You can sift down through the posts here to find common problems with the 97 Volvo's, but I think that out of all the years for the 850's, 97's were the best year.