For my restorations, if I see that the lamp is loose, I replace the socket. If the lamp is not loose, but it is flickering or dim, I clean the sockets with a "lamp socket cleaning stick". But you will find they are not all that helpful with the Ballys of this era as the sockets were cheap and sometimes nasty !

Replacing lamp sockets is not cheap, but you only need to do it once and then never worry about it again.

From a Business point of view, it is a better idea to replace the failing sockets rather than wait for the next service call ! Takes 5 minutes.