My 240's fan switch (manual heater controls ) has been stiff since I bought the car. Today it was so stiff that I could not turn it to get the windshield defrosted. I would like to try lubing it before I replace it, but don't know what to use to lubricate such a switch. Any suggestions? Thanks

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine