Thank you Gentleman Gene,
I was able to find a diagram of the part #4002 at Sears Parts:
KENMORE | Model #72163252301 | MICROWAVE | LATCH BOARD PARTS | SearsPartsDirect.com from Sears
I read somewhere it is a good idea to change out both switches if one of them goes bad. They will send me the Primary and Secondary Interlock Switches for $20 delivered. If your company sells these same parts, I'd prefer to get them from you, so please let me know.
However, I still wonder if there is a mechanical part causing the problem, so I think I'll open up the microwave and take a look at the situation. I understand that it is probably not such a good idea to start spraying WD-40 on everything, especially electrical parts. My general impulse is to either use the WD, or else duct tape! I'll also try to keep the hammer in the toolbox, although that's worked in the past...
Thanks,
Tom