Probably this is an old idea, but just in case: turns out a Q-tip can be chucked into an electric drafting eraser (dinosaur from the old mylar and pen days, lying around many architect/engineering firms), gets into tight crevices. You can use it damp/wet without spraying everything else around, get close to decals, control on/off easily, etc. etc. Suppose you could chuck one into a regular electric drill flexy extension, but haven't tried that, and it'd take two hands.
Reid (about to hear from hundreds there's a better way) Fisher San Martin, California