The E36's one real structural weak point is the rear subframe mounting area — and it's the unibody sheet metal that cracks, not the subframe casting.
Cracks start at the four subframe mounts and the trailing-arm pockets in the trunk floor, and left alone they spread until the subframe can tear partly loose — owners report it as sudden rear-end movement at speed.
Any E36 that's been tracked, drifted, or run on sticky tyres or more power MUST be reinforced, and even a clean street car deserves a look.
Inspect it: pull the trunk carpet and check the metal around each mount and the pocket just ahead of it for cracks, wrinkling, or fresh seam-sealer hiding a past repair.
The fix is reinforcement plates welded over the mounts and pockets — BMW sells a plate kit and there are stronger aftermarket ones. Caught early it's a weld-in afternoon; ignored it becomes floor-pan surgery. A car already torn here isn't an automatic walk-away if you're set up to weld, but price it as a structural repair, not a niggle.