.Rubber mallet does clear it up. Proper disassembly and cleaning is best... but Ive gotten more than a few to work with a small nudge of the rubber mallet. Your mileage may vary.
It is called a "Love Tap" where it ain't working and now it is - and then it gets fixed when the calamity is over I think a lot of these machines sit more than they are used. Contactors will get gummy and sticky from sitting and being exposed to "the elephants of the weather". Contact cleaner helps too but like you said, a tap will make it go again until something better can be done.
Yeah, the elephants (not elements).
Those things that stomp around and knock your stuff over
The building behind us is a Dispatch Center for concrete trucks. They have a CAT generator sitting outside on a concrete pad inside a fence enclosure. They are committed to it working right, so every Friday morning at 0700 the generator kicks off and runs for an hour. Talking to their maintenance guy, the best thing they ever did was to setup the REGULAR RUN and TEST. We are in the middle of town, so idiots in cars knock down utility poles regularly and a functional generator is important to their business.