Second shop also says it is locked up and needs a new engine. Again, not much diagnosis on the actual cause without costing me a pretty penny. Once I receive their quote for engine replacement, I will figure out what to do next. Regarding taking it to the dealer, it has not been serviced by Mercedes since I have owned it, so I wouldn't expect any goodwill. I anticipate selling it as-is unless this other shop is much cheaper than the $15k quoted by the first.