...Thousands of engines were made for 350s worldwide, but the percentage with problems were theorized to be less than 5%.
Actually the figure was 50%. Just peruse the diesel mailing list archives of MBCA.
Nobody knows what happens to these cars, and before it can be fixed, its already too late.
Once the piston has started to ovalize the cylinder, usually the #1 piston, the sleeves (yes, I have JUST found out they DO seem to have sleeves) need replacement, as well as the pistons. One piston being out of alignment for a while, slapping up against the sleeve may cause the piston to eventually break apart and do further damage (pitting and holes in piston). Then, it gets really bad.
Low oil pressure develops in the final stage, and there is excessive wear on the bearings, with the engine being toast. They are garbage when this happens. Its a toss of a coin as to when it will, if ever occur.
I've had the fine luxury of having to live through this, and seeing the shortblock and its internals FIRSTHAND. Its not a pretty site, as the engine was/is my own.
My 350SD just came back today with a used 3.0 liter from an '87 300D. This time, my car is on its THIRD engine.
Screw the 350's. When I first join the mercedesshop forums, I harped about how wonderfully refined and powerful they were.
I feel like I was conned by Molierre's Tartuffe. I've been Tartuffified!