As long as normally scheduled maintenance has been adhered to, including aftercooler and heat exchanger cleaning every other year, they are a bulletproof engine. Split head,sleaved,bypass oil filter= long life. Now thats as long as the engine was not overloaded and was run around 2300-2400 rpms. They are also quiet and smooth as a babies ass. Parts are pricey but its unlikely you will need any. I will say that with 4000 hours you are due for injector checkup/rebuild, if it has not been done alredy.
Have a 1982 TAMD60 with 3,000 hours. Runs perfect. Only smokes on start up in cold weather. Once she warms up, run her at 2300 with no smoke. Cleaned the aftercooler a few years back. Never put a major part on it. [should not have said that] Do not give it a lot of use, but for a 30 year old engine she is Great. An old time classic.