Before we go on with your penny squeezing techniques of MB maintainence of not replacing fuel filters as preventative maintainence because supposedly a dirty filter actually filters better than a clean one (yes I researched your posts), the guy ran Power Service through his fuel system, which has detergent like properties. I'm thinking perhaps the additive stirred up some dirt, giving the fuel system a rather good cleanout and possibly clogging the fuel filters causing power loss and rough running. It's not a load of BS as you say. If he took my advice to change the fuel filters, he would probably check the filters first before working to see whether or not they actually need replacing. If they didn't need replacing, he could just simply keep the others as spares.
-Joe

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.