Starter went at 296K kms, cost $170 for new and I put it in myself, kind of hard because you have to take the intake manifold and fuel line off to reach the screws. Don't see how some ppl says its possible without taking those off. Rust started appearing under the batter tray in the trunk. Some wiring problem caused none of the windows to open or close and instrument cluster bulbs don't work due to that short in the system. Also rear differential mounts cracked, it's a known issue with BMWs. I had to get a friend to weld in reinforcement plates, not a cheap fix if you don't know what you are doing. (Could get charged $1200-2000 from a shop)
Coming from past experience owning a '95 M3, '97 328i and a '95 325is I think this 92 318i is terrific for the money. Great handling (I have some cheap lowering suspension springs), 5spd is fun to drive, awesome on gas (600km / 50L tank). Great vehicle for a student kinda guy who wants to save money, but still look decent pulling up in a bimmer versus some beat up toyota camry.
Are the differential mounts you speak of the rubber flex couplings? If so, I had mine replaced properly by my foreign auto mechanic for less than $200 with no welding/reinforcing required! He did tell me that most people do let them fail, resulting in the need for a new diff, which is indeed expensive, but this is completely preventable. Good luck with yours, I love mine!