I've used W-40 to bring my Trico defroster fan, wiper motor and my vacuum switch for my diff. on my 46 Tow Truck back to life. I played with that diff switch on and off for YEARS! (It's a sealed unit) Finally got it to pull in the WD-40 and it started working, feed it a little more and it stopped leaking. All three units have worked great for years!
