Changing oil and having the rear seal changed are two very different operations. Oil can be changed in your driveway in about 30 minutes. A rear seal change requires the transmission be pulled out to gain access. Lots of special tools, stands and experience required. Most owners live with a seeping rear seal until it becomes a rea LEAK. Note also, if your car is a turbo, the turbo's oil return line seal and gasket fail and leak regularly and while dripping from a different place, might give the impression the rear seal is leaking. Get under the car (on ramps, not the jack) and look around.

Regarding shocks, springs, etc, the shocks and struts can be replaced with any number of aftermarket items from Boge, Koni, Bilstien etc, but know what kind of ride quality you want before you spend a dime. Also, given your mileage, you'll likely replace the mounts as well. Springs I wouldn't change unless you have a sag problem or want to lower the car which I wouldn't do. Just me, my car and my opinion but I don't consider a lot of what owners do "upgrades".

If you do want to lower the car there are several "Sport Spring" options available. Bear in mind you should thoroughly go through the rest of the suspension system given your mileage. Bushings, tie rod ends, sway bar links, ball joints etc. If you do want to lower install a skid plate under engine.

If your's is an automatic, changing the ATF is a good idea yearly. I wouldn't recommend a power flush but just a change. The procedure can be found at Volvospeed.com go to Bay 13.

Hope it helps,
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Erwin in Memphis, '95 855t