You could consider trying the conductive silver paint sold for PCB track
repair.
There is a certain art in using this.

It is generally NOT conductive when whet and relies on the nonconducting
binder evaporating away and leaving the silver in contact. Once you have the
knack it makes OK PCB tracks.

May be incompatible with your rubber though ???




      Russell McMahon
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From: Lee Jones <lee@FRUMBLE.CLAREMONT.EDU>
>I'm looking for a small quantity of conductive coating to
>repair a rubber membrane keypad.  I got some oil between
>the rubber membrane and the PC board.  Alcohol cleaned off
>the oil just fine.  But my overly vigorous scrubbing with
>a Q-tip also removed the conductive coating on a few keys.
>
>This is the style of keypad where there are interlaced
>fingers on the printed circuit board.  Underside of each
>key is a dome of rubber with a raised spot in the center.
>The raised spot is coated with a conductive substance.
>When the key is pressed, the conductive coating closes
>the circuit by "shorting" the fingers together.
>
>Anybody know if this conductive coating is available for
>repair work?  If so, a vendor and part number would be
>nice.  Or is this material the exclusive province of the
>people who make rubber membrane keypads?