2012 A6 with 49K Miles started running rough at idle. Reputable shop diagnosed as valve timing chain on driver's side having slipped. Say they have to drop the engine to repair. Bill around 5K. They have eliminated spark plugs, vacuum leaks, injectors and PCV valve as possibilities and shown me with an Audi tool that the chain is displaced. Because valve chain cover is at back of engine, they say they cannot repair without dropping engine.

Does this sound right?

Joel