Mike (et al),
I found that using a q-tip and Rubber Renue and then a quick wipe with a clean cotton cloth will get those contacts working like new.
We used to have to do it at my first repair company for people that liked to drink acidy, syrupy things while working at their computers and weren't all that good at hitting their mouths.
Rubber Renue (has many names and spellings) can be found at any place that services VCR, tape decks, turntables or electronic parts suppliers and is used to resurface the rubber belts in many A/V components.
I think in my case I am suffering from poor conductivity. But "Rubber Renue" (or something like it) sounds like it should be in the bag of tricks. As the machines get older the rubber parts definitely dry out and deteriorate.
Mike