There are five engine mounts on the 850. I replaced all of mine at 165k.
Signs of bad mounts can be excessive wiggling around of the engine, although mounts in very bad shape (like mine were) can lead to no engine wiggle since it's pretty much connected right to the frame. in this case you will probably really have to really push on the engine to get it to move. But when it does, it will move alot. One of the easiest tests you can do is put the car in park, and roll it back and forth. As the transmission resists the turning of wheels, it will torque the engine and you can monitor the motion. Any kind of excessive or clunky motion may indicate bad mounts. Good mounts should allow for some engine movement, but the motion should be controlled and not excessive, with firm resistance to movement provided by all the mounts.

There are three that do supporting: a front one under the starter, a rear one under the exhaust manifold (or turbo), and one under the crankshaft pulley next to the right tire. There are two that resist engine torqing: the obvious one on top of the engine, and one on the transmission under the engine near the oil pan.

Both the torque mounts are easy to replace; the one on the top of the engine is junk: immediately buy an aftermarket urethane one on ebay or from IPD and you won't have to worry about that again. The one on the transmission is easy to get to, and easy to replace. On both the torque mounts, you can easily see their condition, as they rip when they are bad. Try shining a flashlight through them to look for rips.

The supporting ones are hard to get to. The biggest problem is compressing them. I'm thinking there is some kind of dealer tool for this, because I had a very tough time trying to squish them down (and I consider a full front suspension re-do was no big deal). They are filled with a hyaudralic fluid so, be sure not to puncture them (although it is an effective way to shrink the old ones for easy removal). The one near the crank is easy to get to, but the bolts are a real pain. You can't get a socket on them, and you can't get enough leverage with a crow's foot wrench. I think I had to use a stubby bent box wrench or something to get those out.

I recommend replacing the torque mounts yourself, and let the dealer replace the supporting mounts, unless you're up for a challenge.

Hope this helps!

Jason S
'94 850 Turbo wagon 205k