FWIW, we had several dozen complaints about the M272 engine knock. all were resolved.

I can see why you would doubt the ability of a shop that requires technical assistance from the manufacturer but you can't see the entire room by looking thru the keyhole. Here's how it works in the real world. No dealership would attempt a repair of that magnitude and expense without seeking advice from MB. We knew it was a bottom-end knock, that was easy to figure out. The question is what to do about it. Maybe there's a crankshaft issue we're not aware of. Maybe an oil pressure glitch that won't show up on the gauge (yeah, we checked that first)It would be irresponsible of us to tear down a motor just to "have a look". Why didn't we just replace all the bottom-end bearings you're probably wondering? Without the critical piece of information about using bearings one size tighter we would have done a hell of a lot of work for nothing. Why didn't we try tighter bearings and see what happened? What if the motor blew up? Guess who's paying for that? Not MB I can promise you! So we gather as much information as possible and pass it on to MB technical. Let the engineers figure it out. That's right, the engineers. I'm not an engineer and I don't have an engineer in-house. If they say install tighter bearings and the motor blows up then it's their problem, not mine. Sorry, but I have to protect the company I work for as well as satisfy my clients. I hope this clears up any confusion