WD-40 isn't going to do much for a Benz safety switch -- all the ones I've seen are sealed well enough it would only get inside if the seals are already so bad water is going in.

Should be pretty easy -- pull tranny lever, unbolt switch (three screws or bolts), replace tranny lever and probably put a new plastic bushing in. Adjust siwtch and drive away. Only real difficulty I've ever had was that the top screw was a bear to get out -- replaced with a hex head rather than a screw slot type.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!