"The M108 /M129 engine wasn't the best one MB built. It was prone when new to eating pistons and having many problems in service. It evolved very quickly into the much better but still sometimes problematic M130. The M114 250 motor is actually quite different in terms of piston and ring design to overcome those problems. Over the years I've been working on these I don't recall one original standard M129. I've seen plenty of unopened M127 and M130.
That reputation follows the cars, even though any surviving 250s are all fixed now." - Chris Stewart, FB 25-Aug-2023