as I was saying, I don't want the slab to act as a reservoir that slowly releases toxins to the copper coin; if the slab material is capable of doing this...
I completely agree with you. In my case I was so taken with the coin I couldn’t bear the thought of parting with it for several weeks for a re-holster. I also couldn’t stand the thought of enjoying my coin through the horribly scratched slab. So I took the risk and polished it being very careful to apply small drops of the solution and staying away from the edges of the slab because I had the same concern about chemical seepage onto the coin. That was back mid July and the old cent is fine. But I 100% agree that a re-holder is by far the best way to go about it.
It does work on NGC holders, but not as well as on PCGS. Probably because of hardening additives in the compound used to mold NGC holders. A double-edged sword . . . Because it's harder to scratch them, it's also harder to remove scratches from them.
Reholdering is the first reflex but NGC only guarantees the grade (MS65 RB) up to 10 yrs from the grading date. My cent was graded in 2005. If I could show some high quality pics I would. Anything less would solicit uncertain responses.
The holder is damaged. Why try to repair a piece of plastic? Send back to NGC for a new slab or cross it over to PCGS. Better for the coin and the owner.