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The nubs are fine, it will not hold vacuum, the seal is apparently worn out.




They use a light coat of grease on the slider,it dries with age and won't seal.If you are careful you can take the switch apart,clean it and use a good quality grease.You can take it apart and put it back together with a little common sense,did mine years ago and it still works.Also,there are a lot of sources for leaks on that system,hoses,check valve in reserve can and headlight actuators.Get a hand vacuum pump and eliminate them one at a time.