Don't know the specifics of the 603 in the W140, but you mentioned that the wastegate was vacuum operated, and, additionally, that the door locks are inoperative.

So, this tells me that you have a vacuum leak somewhere. Get out that trusty Mityvac and start running the system. It should hold vacuum on all circuits from the vacuum pump, with the exception of the transmission vacuum control valve on the injection pump. You need to track down and plug the leak. When you do, the door locks will function, and the wastegate might function as well.