Are you using some sort of de-greaser to clean your bike? As a technician, I have seen similar "mystery" rust in unbelievable places on other bikes in the past. I have found that some de-greasers can leach away lubricants a little too well, and can cause rust. Some hard-alkaline, or acidic de-greasers will cause etching on both ferrous, and non ferrous metals. The absolute worst case of "mystery" rust I have ever encountered turned out to be caused by a cycle owner using a steam cleaning pressure washer.a bit like this
+1Are you using some sort of de-greaser to clean your bike? As a technician, I have seen similar "mystery" rust in unbelievable places on other bikes in the past. I have found that some de-greasers can leach away lubricants a little too well, and can cause rust. Some hard-alkaline, or acidic de-greasers will cause etching on both ferrous, and non ferrous metals. The absolute worst case of "mystery" rust I have ever encountered turned out to be caused by a cycle owner using a steam cleaning pressure washer.a bit like this
+1 on degreaser type cleaners... They can and will cause metals to corrode including aluminum.i have seen simple green or greased lightning do that too peoples bike that may or may not detail the bike... might as well upgrade to pazzo's i just did and i like them plus they are black...