I have a similar arrangement with the local jiffy lube as does Tom W, however without the manager's adoration of my wife. They use my filter (Mann or Knecht) give a $2 filter credit, and let me watch; sometimes I can even get in the pit to see the underside of my 94 E320. I ask for Mobil 1; they pour from the can; 2 years running without any, repeat any, trouble.
regards,
Mark