Have you tried an electronics supply store? I doubt that Mercedes made those plugs, they will have sourced them (or whoever built the boxes would have) you might find a brand name on the box that might help. Kinda like Volvo radios made by Alpine. Everybody is making those 6-pin electrical plugs - you might get lucky? Otherwise, cannon plugs might be the way to go.

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1991 300 SEL
218,000 Km

"Xsbank's rules of mechanical intervention: Always go for the easiest solution first; 90% of what ails a gasoline engine is ignition; After that its all a WAG."