The first Mercedes Diesel engine we ever overhauled was a 1975 240D, the old girl had been left for dead. That got the ball rolling and since then the engine rebuilds and complete refurbishments make up a very long list. It would take some time to list them all, but they range from the older four and five cylinder naturally aspirated Diesels, up to the newer Turbo charged aluminum head six cylinders. In the past few years we have put a number of Diesel and gas models back on the road, years range from 1975 to 1991. We have enjoyed almost every minute of it.
Preventive maintenance is as important as regular maintenance.
A good repair shop, be it a dealer or independent, will keep you up to date on the parts that need to be replaced prior to their failure. Your technician may not have a crystal ball but for the most part he knows the life expectancy of the parts on the Mercedes they work on. Trust is the key to the relationship between you and your repair shop. There are always exceptions, not all shops are honest and not all customers are either.