I'll probably just leave it as is right now. Unfortunately, the bubbling is on both sides of the fender and it is right on the line where the two halves meet. Therefore, if I grind it out, I'm going to have a hole since the rust goes all the way through. That would involve getting out the welder and welding a patch on, which is going to be difficult to do without welding the two halves together and having an odd looking patch. I'm in the process of building a house and just don't have time to go through what it's going to take to make it look right.
After reading some of the posts here, I'm finding it hard to conceive what they could have exposed this tractor to in order for it to rust so badly in such a short time. I'm starting to wonder about a manufacturing defect. Especially since the rust is only isolated to a couple of spots on the fenders. If the former owner would have been rolling through salt water, I would think the whole fender would be rusted out not just a few spots.
I highly doubt if Kubota is going to fess up to any defects, but I don't know. What kind of warranties do these tractors carry on rust, if any?