So the rod is out. Using a machinist's straight edge (two, actually) I can tell the big and small ends are not parallel, and the error is in the direction that would explain the canted piston. For $60 bucks, I've bought a set of rods from a OM617 turbo parting out, and will find one that is the same weight and see if installing it causes the piston to sit properly. Other than matching the weight, any other advice would be appreciated.

But here is the mystery (to me at least). Along one side of the old rod are handwritten numbers that don't appear on any of the other rods. Every engine tells a story, and I'm wondering if this is normal (weight, maybe?) or if someone has been in this engine before, or if some "adjustment" was done at the factory. I have heard stories of manufacturers intentionally tweaking rods to account for boring errors, but that somehow doesn't seem like the Mercedes way. Also, the piston is slightly worn on the offset side, indicating that this has been the running condition of the engine for a while.

Any guesses?