As far as the anodizing being marked up, what type is it? Are you talking Stealth coating? That can usually be cleaned up with some heavy cleaning as it's just transfer. I'm not sure about the stovepipes, but I believe that's indicative of shooting technique in some of these smaller guns. (Somebody correct me here if need be).
As for UMC...well, it runs in my HK; BUT it is FILTHY...makes WWB look like Gold Dot clean. So, if you've popped off 60 rounds of UMC, I can see where you will run into problems with filth, causing the guns to malfunction.