I am almost positive mine is a result of a huge pot hole impact on an already blown strut - the hole was so big and there was no fluid left in the strut that the strut tower took the impact (as well as my bent allot wheel) that the sealer cracked and water from car washes etc had gotten in there. Several months later the rust started and the rust ring around the strut tower started. Mine was actually worse than 2006aveo - not that this is a competition I wish to win. As soon as I saw this thread I went out to look at mine and -f.uc.k I found it. My neighbour who is a contractor welds a great deal of stuff and fixed mine up for me (free) and now the car actually feels sturdier in the front end. I put several coats of undercoating on it as well as took some chain lube and spayed up inside the strut tower. So 2006aveo if you have had a hard hit to the passenger side it may be the start of it. Here in Ontario a great deal of salt is used but the hit is just a theory. Anyways thank for making me look and now it is fixed. Christmas greetings to all!!