I contacted Waxoyl AG.

She supports my Mercedes-Benz Owner's Manual that is against postproduction rustproof treatment.

A shop owner in the UK who has been applying Waxoyl for tens of years expressed the same opinion.



My MB manual:

"Your vehicle has been treated at the factory with a waxe-based
rustproofing in the body cavities which will last for the lifetime of
the vehicle. Postproduction treatment is neither necessary nor
recommended by Mercedes-Benz because of the possibility of
incompatibility between materials used in the production process and
other applied later."

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1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.