@newyork13 ... I'll second the Magic Rub. I mentioned the Ruby Red (which I don't have on hand or have misplaced) and couldn't remember the name of the other one at the time of my earlier post. Later that day, I dug "the other one" out and cleaned some center posts LOL.
I like the Magic Rub 1960 you use best, for the form factor. Peel-off 1960 is much handier than this Faber Castell Magic Rub 1954 for cleaning ProVari contacts. Both are the same Magic Rub material, just different vendor and form factor. I can also visualize the Magic Rub 1960 reaching the positive contact on the ProVari tube
mod circuit boards too. I use this one only because I've had it around a couple of decades and used it ocassionally when I worked on PC's and various circuit boards. Magic Rub doesn't degrade or dry out, harden like pencil (type) erasers either.
Magic rub description: Magic Rub Eraser is a white vinyl non-abrasive eraser for mylar drafting film, delicate drawing or tracing paper.