I recently purchased a bunch of proof sets, 1970-1992, and under a magnifying glass, I found that while I tried to avoid obviously tarnished coins, other coins looked to be in danger of becoming damaged. Several coins inside the lenses have an oily substance on them or loose felt from the packaging. So far, the coins don't appear to be damaged, but if I act quickly to clean them, I might be able to prevent future damage.
What should I do? My main goal is to keep the set together so I can sell it later. I have read around here about parting out sets when single coins get high enough in value. Would the set still have value uncracked but with one or more bad coins?
Thanks in advance.
Example of oils on 76 Eisenhower through plastic case:
