suggestions on backplane cleaning? (or, HP2100 continued)

One major problem with my 2100A has been solved (sort of). I had a card that wouldn't work properly in a particular slot, finally got the bright idea to move it to a different slot (I'm using polled mode, not interrupt, so this is possible). The card works great. Problem solved? No..... In the troubleshooting process I noticed a few slots that no cards would quite work right in. I checked the back of the backplane (it is a hand-wired backplane), no loose wires, etc. After very close inspection of the backplane slots, I determined the problem is the contacts are dirty/corroded/whatever. I tried the best I could to clean the contacts inside the slot, but this is virtually impossible. I also cleaned the card edge with an eraser just to be sure. Bingo - card now works fine but only in the cleaned slot (or one that worked previously). So, given that it's a delicate hand-wired backplane, does anyone have any magic tricks for how to clean the gold contacts inside of the backplane edge card connectors? I'm afraid to experiment and looking for wisdom... :) Thanks! Jay West