I just rebuilt my forks a few weeks ago and I too had some corrosion on the tubes. Mine was thankfully above the sweep of the seal... where the springs ride.

I like the JB-Weld idea... I'll keep that in mind should I run into it again... especially across the seal sweep area.

I acid treated my corrosion (makes the rust inert) and greased them up where the springs ride.

Gotta keep water from getting under those rubber boots. The design of the forks gives water a place to sit below the spring seats around the seal area.

Happy Trails!