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I took my A8 to a local independent garage to have the timing belt changed and they bent a valve, according to them.  To repair the problem, they are swapping my 104000 mile engine with a 60000 mile engine.  The repair has taken over two weeks now, but they say they can do that much, much less than taking the car to the Audi dealer to be fixed.  What should I look out for when testing the new engine?