I think you've really got to be diligent about removing all the old seam sealer and absolutley get rid of as much corrosion as possible. It's all about the prepwork I think.
If you use the SEM two part self leveling or something similar, you've got to work fairly fast as it sets up and cures fast. Seemed to work pretty good, I just wish the working time was a little longer. Also, you need a special applicator. My paint store gave me one to use, just had to leave a deposit.
There's some recent threads on this topic. You might do a search.
-David
