Standard body seam sealer will shrink & crack on a joint like that, we use a flexible bonding mastic (Sikkaflex) & never have any problems.This doesn't shrink with age/curing like seam sealer & will stay flexible enough to cope with any body flex. We carefully mask either side of the joint with tape, squirt the mastic into the joint & then wipe off the excess with panel degreaser (pre paint wipe) & remove the tape, leaving a factory finish prior to paint.If you want a factory finish this is the way to go. Hope that helps
