I have a key-fob which hasn't worked for some years, but have just seen an advert for replacement rubber pads and micro-switches.  I had a closer look at the switches in my fob and noticed that they appeared to be gummed up with a green material that was probably lubricant 10 years ago.  I applied a little penetrating oil to each switch and after a few gentle presses they came free.  Fob now works again.  Suspect any light lubricant such as WD40 would work as well.  I put a little vaseline on each switch to maintain future lubrication.

This is a handy tip. 

I, like many others I suspect, tend to use one fob all the time, with the other remaining in a drawer. I try to remember to use the other fob a couple of times a month, in the hope that use will stop the buttons gumming up.