When you engine wears out - look seriously at swapping in a different engine
Can you put a turbo engine in a non turbo car? Can you put a 300D engine in a 240D? Can you put a W123 diesel engine in an older W115? Follow Kent's video series listed below to find out what you can and can not do:
Problem & Solution
Common among these chassis:
W115
W116
W123
W126
Mercedes Diesel Engine Swaps Between Chassis and Models: Introduction: https://youtu.be/i9Yg8YF2u0c
Mercedes Diesel Engine Swap Advice: OM617 Non Turbo into a W123 240D https://youtu.be/aTCR0IZ9hnY
Mercedes Diesel Engine Swap Advice: OM617 Turbo into Non Turbo W123: https://youtu.be/-OC4G058UU8