i had the same problem earlier this year on my 81 380sl. The 4 Seasons drier does have a smaller opening for that switch. Its 6mm, vs 9.5 on the OE, and Santech makes one that fits.

I know because I ordered a new one for my Behr drier, and I had to send it back because it was too small. Yet it will come up as fitting a 380.

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1981 380SL
Chassis: R107.045