For my upcoming component guide of the GT/TE I have this:
If the conductive part of the rubber fails to be conductive even after being cleaned with alcohol,
Conductive Wire Glue can be used (www.wireglue.us) try to avoid conductive ink as it flakes off in time.This can also be used for the pcb in the circular pcb pads as it's actually related to what nec used when they made
the pcb, you just have to be very careful as the circular pads are very fine and small, if done with care you may never notice
a optical difference upon inspection.
This is also used on some of the controllers for autofire (a couple black square parts) and some other controllers from this era,
some use circular pads in tin/copper and some use goldplated, but a lot of them use this very type of conductive pads.
Cheap pirate controllers conductive pads is dissolved with alcohol, both on the pcb and rubber pads but never seen it happen
on the big companies controllers (nec/nint/sega.