Guys, I'm also having trouble with the copper on my pass-thru for my ProVari. The citric acid and/or eraser sounds good.
BUT, my pass-thru is only a few months old and it's already showing signs of brown stain which is not allowing it to make good solid contacts. So, is there anything that I can use to keep the stain away after I clean it? To protect it so that it's not likely to stain so quickly?
Thanks.