My D.R. ceiling fixture has 5 sockets. When changing bulbs.
I noticed that one socket did not work. I shut off wall switch; tried
unsuccessfully to look inside socket; swabbed it out with old
toothbrush *; sprayed with Cramolin (used for audio equipt),
but no luck.

Any educated guesses on why one of 5 would have crapped out?

And what is best approach to reviving it?

TIA

Aspasia

* old toothbrushes are very handy for all kinds of odd jobs.