I can pass on what my mechanic and other MB owners told me when I bought my 87 300E. They said to maintain it on time every time, don't be late on the coolant or brake line flushes, only use high quality MB recommended parts and fluids, change the oil about every 3000 miles, and keep organized records. The cars are supposed to be pretty sturdy when maintained well, but failure to follow the schedules allows a cascade of problems. Example - my dad hadn't followed the brake fluid or coolant change schedules. result - a corroded water pump that was leaking and needed replacing before it failed and took the heads/block to Valhalla with it.
87 300E, 65k miles