Quoted from homebrood:

I have a couple classic Bally's and I did a trick I read about with skeptisism but thought I'd try it.
I put a drop just one drop of three in one oil on the fiber spaces of all the sockets, the fiber slowly absorbs all the oil and expands tightening up the socket and making them work solid again. It absolutley worked on two games! All lights have been fine for like three years since!!! Took just a few minutes but you need to let it sit for a week or so before you realize all your lights are working again! The oil does not make a mess and dissapears into the fiber within a few days! Whalla!!! Sounds weird but it works!!!