The W115 chassis is beautiful to drive and mechanically simple. However, as others have mentioned, very prone to rust and at that age, in need of full suspension rebuild to bring back the great handling. I wouldn't pay much for an unrestored one...
The W123 chassis that came later is the one that is more "bullet proof" if you are looking for longevity. W126 is good, too...
Cheers, Andrew Seidel.
85 500SEC Lorinser
83 300D Turbo