Rust in the floors, rails and shock towers
Underneath, an E30 M3 is an E30, and it rusts like one. Specialists and Hagerty's guide list the trunk, the rear quarters, the cowl and the edges where the windshield is bonded, the sunroof drains, the frame rails, the floor pans, the battery tray, the rear subframe mounts and the shock towers. Repairs range from small patches to structural work, and some M3-only body parts are expensive or no longer made.
How to check
Put the car on a lift and check the floors, rails, jacking points, shock towers and battery tray, then look under the trunk mat and around the windshield and rear window for bubbling paint.

