On Wednesday, November 23, 2016 at 8:03:45 AM UTC-8, Doug White wrote:
I have a couple small magnetic-base gooseneck work lights mounted on my
milling machine. They were designed for 20W 12V MR-16 halogen bulbs,
but... I switched to LED replacements

They have C&K garden variety 6A 125V slide switches...
the switch on one became intermittent....
Just recently, the switch on the 2nd light has started exhibiting the
exact same symptoms.

If you can detach the power supply, try running the switch with a 120V
incandescent lamp as its load (60W to 100W bulb). It's possible some
small amount of oil or dirt is coating the switch, and 100 mA isn't enough
current to burn it off. The polymers in a switch, or grease that makes it slide,
can outgas or seep into the metal/metal contact area with distressing results.
That switch is supposed to handle higher voltages and currents, and might
be self-cleaning if given a chance.