One other thought about the "rust" and "contamination". If Chinese drums are like my experience with Chinese rotors, it could just be the drum sucks. I quit buying the cheap-o Chinese rotors. I've had some where the outer face looked 100% fine, but the brake worked like you had warped rotors. I pull the rotors off (just a little over a year old) to find chunks of metal missing from the inside face. One or two times of that was MORE then enough for me. Perhaps your drums are doing the same thing.

Keep in mind, drums and rotors on modern cars like your Monte are not really meant to be resurfaced/turned/sanded. Typically when you are to the point of having them turned, it's just more cost effective to replace them.

 

I mean they are the origninal drums they work like new again i only noticed dimished braking power and faint barely audible grinding from drums he checked brakes at all 4 corners and the drums were the culprit after repairs he drove it to make sure. just as a warning he's a GM Specialist his two dd i see are a 90's tahoe and a seafoam green colored olds cutlass (wbody w/3100) it could be something related to why the e brake locked up and it was left to sit.