I know I am going to take some heat for this, but be that as it may.....I was washing my 6 and my fiancees 6 today and looking at the channels of the doors which I found the rust/staining issue with. I decided just for the heck of it in a few spots to scrape off the "rust" with my finger nail and you will never guess what I found under it.....PAINT! Not exposed metal with left over rust residue as you would expect if the car were actually rusting. I even scraped the area at the end of the channel and noticed that on the spots that were totally wet the substance actually came off kind of sticky and almost looked soapy. I found this on the few spots on both cars. On spots that weren't wet the substance was hard and kind of flaked off, but had clean paint under it. This is not what you would expect of a surface that is rusting, the paint would be gone! I don't work for Mazda, so this isn't propoganda. I just think based on what I found today that it is reasonably possible that this isn't rust and is actually something that is dried out and is a rust color. Flame if you may but check for yourself.........