Rusty46,
thanks for the information. In my particular case, I reached the point where the metal is stable and the low area is small enough for filler. However, the frustration remains, at not understanding what is going on in the process. One of the really difficult things that happened to me was as I worked the area, the problem seemed to spread and get larger very quickly. I now know what was happening but it was very difficult to figure out at the time. Of course, I am an amateur and a professional would know how to tackle it right away.
