The particular catalytic converter problem described is unlikely to be an issue for a Mercedes.
The RX7 rotary engine is a very special beast indeed. One of the many things that sets it apart is that a certain amount of engine oil is deliberately injected into the combustion chambers to lubricate certain components. The exhaust therefore contains an unusually high concentration of unburned oil, which may create 'downstream' conditions you would not typically see with a conventional 'reciprocating' engine.
1986 300E 5-Speed 240k mi.