Well, there was a thing from Gotham that said you could put distilled water on the capsule and use a very, very soft brush around the inside edge. The purpose being that you are not really touching much of the gold, and you are removing the dust and stuff that will capture moisture, and act as a conductor between the center termination and the edge, which will short the capsule until the moisture evaporates. It does work, the chances that you are going to screw the pooch are high, as well.
I have been of the opinion that unless the capsule is just absolutely filthy and weighted down, a particle or four of spit is not going to matter that much. If it sounds wrong, and it's shorting out with the breath test, then send it to a pro to clean.
As far as cleaning it himself, I'll say this Billy, don't be a hero!
BTW, I found this schematic. I can barely make out the word "Sprague" in the cap section, like after .47