looking at the front end before you ripped it off it looked like it had quite a bit of filler in there as well, bonus on getting rid of that!
and as others have said, literally ram paint into that seam before you go over with sealer, and on the back seam as well, before sealing that also! and for sealing, run a bead into the seam, then run your finger along it, pressing it in, but without removing the seam completely and making it look de-seamed:) and when you dont, let it go tacky ( not dry completely ) and then put primer over it. you do this becuase if the sealer was dry, the paint wont stick to it, and the paint will crack after a few months. if paint is applied when the sealer is tacky, the paint sticks and flexes with the sealer when you are driving along. the paint will not crack:) bit of a tip there for you
what are you going to do about the corrosion on the inner wing, flitch panel and floor where the subframe mounts, it may all be surface rust now, but you may be replacing that front end in a few years time if you dont conquer it now!
