Motor mounts
Mount location pic. It behooves you to keep an eye on the front mount and replace it if it fails; otherwise, the damage spreads further and you have to replace other parts. You also need to keep an eye on the torque rod. It's in plain sight at the top rear of the engine, so it's easy to keep an eye on. If the torque rod bushings fail, the front mount will fail too.
Any time that I have the fender well liner removed, I check the mounts; yearly at a minimum. Here's how. Clean off any oil that's spilled or dripped on it, as well; it's said that oil attacks the rubber. You should be able to see any failure coming. The front mount tends to separate - the top of the rubber part pulls right out of the base. Some people say the engine bangs around then, but mine didn't - the shifter just moved more than usual under load changes (the shifter moves quite a bit anyway).
The rubber in the front mount is allowed to stretch vertically as much as an inch, and there-in lies much of the problem. There is a limit bracket to stop vertical travel at that point, but Townsend Imports recommends cutting the travel to about 3/4" or less by screwing a piece of split air conditioner hose to the mount limit strap. I took it a step further by screwing a piece of AC hose intact to the limit tab. This cuts free travel so a very small gap so the engine is allowed to idle normally. When the engine is loaded, the AC hose acts as a buffer to limit the travel and absorb shock. See link to my mount mods on the next page (Mount Replacement Notes page).
So how often does the front mount fail? Mine was shot when I got my 91 9000 turbo at 67000 miles. Maybe every 25000 miles if you're a slam shifter. Maybe 50000 miles if you just drive hard. I think that if you do my mod, they should last a long time.