Need opinions on possible engine damage.

[cdavidson]

All I wanted to do was stop an oil leak on my 1994, S350 TD (213,000 miles). I took the car to a non-dealer but experienced Mercedes mechanic. The "bad head gasket" was quickly identified as a cracked head (a well known design flaw in this engine). I had the mechanic check for bent rods and cylinder wear. Everything checked out fine. I said go ahead and replace the head.

Several weeks later I get the car back. It went 70 miles before "blowing up". The #1 intake valve dropped into the cylinder and broke up. Parts blew back into the intake manifold and went through the #5 cylinder. Obviously, major damage.

The mechanic rebuilds the engine on his dime (of course). Several weeks later I pick up the car. It goes 550 miles and blows up. This time it looks like the #3 cylinder had a valve being struck by the piston. The engine had a ticking sound like a bad lash adjuster, but it was not loud. Anyway, the disk/puck that the cam pushes against shattered, the cam broke, at least one cam journal mount broke, and that's what was apparent with just the valve cover off.

My question is, doesn't all this trauma to the engine have a high probability of causing unseen damage to things like the crankshaft, main bearings, rods, and anything else that's an internal part of the engine?

Also, the new head was setup by a shop that specializes in diesel engine work. On the first failure, they claimed the valve dropped because a "spin" weld on the valve stem just below the point where the valve keepers engage the stem, failed (act of God, not their fault). Anyone got an opinion on that?

The same shop assembled the second head. They haven't responded yet to the latest failure.