Nice to see that coin in such good condition and the owner had the foresight to put it in an airtite (I’m assuming right away). I made the mistake of leaving mine in the original packaging it was shipped with which has caused it to have quite a bit of toning, especially on the gold highlighting. I’ve never tried cleaning it off, but I wish I had changed it’s capsule immediately.
I did the same thing as you after purchasing during game day. Left it in the original package for a few years before shipping it off to ANACS to be graded. They removed some of the blemish, but I personally like the way it has toned. Mine came back MS64
Good luck to seller, and congrats on a nice looking coin!