Could be an alloy mix issue, but I wonder if it isn't PVC residue or a similar surface issue. Maybe a candidate for an acetone bath first?
Also, what's up with that giant chunk of rim missing at UNUM?
"If you climb a good tree, you get a push."
-----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed."
-----King Adz