and while silver should be good, as we all know silver tarnishes and turn black over time
Oxidised silver is still a good conductor though. In my boring day job, I deal with products which use screen printed silver inks to produce flexible circuits and medical products on polyester - so I know a bit about silver tarnishing!
When printed silver is exposed such as part of a connector to go into a ZIF socket, we often overprint it with carbon. This is largely a cosmetic thing to keep customers happy as they don't like to see tarnished silver no matter how many times we tell them it's ok!
Rather than jumper across them I would just replace any faulty jacks with new ones.
It's not the jacks I hard wired, it's the inter PCB connections which are on pins and crimp sockets (Molex? - or similar). Cut off the crimps and solder the wires straight to the pins and the problem goes away.
It makes it a bit trickier when something else needs repairing - but invariably, that would be done by me as well!