I bought a Magma mold off of eBay for my Master Caster. Fortunately, I didn't need it desperately because it was old and sad. I have been trying to get it to drop usable bullets on and off for a while. The mold cavities seem to be rougher than my other Magma molds. I've tried cleaning it with everything from mild soap and water to oven cleaner. No change.
Out of desperation I dropped it into a container of Evaporaust and left it overnight. The next morning I was surprised to find the solution had dramatically changed color. It was very cloudy and contaminated.
I fished it out, a black slime covered it. I cleaned it up. At least it looked better. Was it a miracle? Nah, it is better though. At least it did something. If I pay strict attention to my casting speed/temp I can get OK bullets out of it.
The better answer was that Evaporust didn't hurt it. I'm not sure I would recommend it for routine cleaning but for problematic molds that are less shop worn, it may well be a pretty good answer.