They all did that. It's been discussed many times both
here and upon the Mercedes mailing list. General concensus
of everyone who knows these cars is to avoid them - it's easily the worst engine MB has ever designed.

Actually, yours seems to have lasted longer than most. Typical milage for failure is in the range of 75K-100K.

I frankly don't believe your dealer has never seen nor heard of this problem. They didn't sell a heckuva lot of 3.5 liter diesels, but of the ones they did sell, very many have bent rods, destroyed blocks, etc.

Try searching Mercedesshop, or try the archives of the Mercedes mailing list at http://www.mercedesmailinglist.com