Timing Chain on a 300E

Next time you have the valves adjusted it's an exta 5 minutes to check the chain stretch. If t's above a certain amount (10 degrees off the top of my head, don't take that as an authoritative figure) then repace the chain. I usually replace the tensioner too, cheap insurance.

Unlike cars with timing "belts" a timing chain does not have a finite service interval, but as said, it and the chain tensioner/rails, should be checked. Usually, the tensioner starts to fail long before the chain stretches out of spec. A good test is to listen to the engine on start up. If you hear a chain rattle at startup that disappears when the oil pressure builds up a few seconds later, that's a classic sign that the tensioner should be serviced.