Some say that Diesel Purge should only be used as a remedy such as when you have nailing or knocking instead of preventative maintainence. Personally, I'd go ahead and purge the system, if it doesn't help, it won't hurt.

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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.