It's awfully easy to over-complicate things for the sake of over-complication. The start contacts in the ignition switch were designed to handle the current to the starter motor solenoid. There are millions of cars of this vintage out there still reliably starting day after day with the same ignition switch they left the factory with. If the ignition switch gets to the point that it is worn on the start contacts, the rest of them are about ready to go too.

Just my own 2˘

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]