I've got a few keyboards where I need to go back over the traces, especially where the traces on the flexible plastic meet the traces on the circuit board for the keyboard. Does anyone know of a reasonably priced alternative. Pencil graphite seems to work, but it's very temporary. Is there something I can use that won't cost me twice what all the keyboards are worth but is relatively permanent?
You could try conductive epoxy. Or Nickel Print, which is a conductive paint marketed by GC Electronics. I use it to paint the cavity of electric guitars to shield the guitar electronics.
I've used the rear window defogger paint on CPU's in the past, it works pretty well, and is easy to apply. I would think it should work fine on flexible PCB's as well.