Glad to hear there are some Mecgar mags now available. The US made mags that came with my XL would turn a paper towel rust brown every time I wiped them down, and that was even when they were coated with CorrosionX. That was just from laying around in open air, not even sitting in the warm moist environment being carried IWB. I've heard of some people have sent out their mags to be coated or using something like Renaissance Wax to stop the rusting.
Didn't you also have an issue with rust on the slide around the sights? The magazine button is another area that people sometimes have problems with.