it seems to slip a lot before engaging the stop, almost as though the switch itself was loose or something. Have you ever encountered anything like that with one of these?
Most likely the knob has a loose set screw and is slipping a bit on the shaft. Next likely is a dried out detent mechanism. If you look at the front of the switch immediately behind the mounting panel you should see a disk with a series of holes around the perimeter and a ball bearing trapped under a circular spring. That's the mechanism which gives you the click (stop) click (stop) feel of the switch. If the grease has evaporated, hardened or become sticky you will loose some crispness in the switch action. Clean out as much of the old grease as you can with Q-Tips and WD-40 (or mineral spirits) then re-lube with something like a black molybdenum (light Lubriplate) grease. Rotate the switch to work the new grease into the detent mechanism until it has a light coating all the way around. A drop of oil on the shaft wouldn't hurt and there's no better time to do it. Remember that with things like this it's better to WD-40 the Q-Tip and use it like a wet swab than it is to blast the area with WD-40 and try to clean it up like a slob.
Do this reasonably well and the switch will live a long and snappy life...
