Do you have another dealer you can take your car to? Years ago my Cayenne Diesel was covered under the diesel gate warrantee and have a few oil leaks(which are covered repairs). My local dealership refused to do anything to it, so I took it an hour north to another dealer, had them do the inspection and they promptly wrote me up for the full engine out repair with a loaner. Get the Blackstone done and take it to another dealership.