Factory seam sealer??

The factory used lead for cars with painted tops, and body filler for vinyl top cars. The best thing to do when you rework it, is to sandblast the seam where the top and quarter meet, and then coat it with GOOD epoxy primer like PPG DP90 or SPI epoxy primer. Then use the Tiger Hair or 3M stuff listed above to smooth the seam. A good base coat of either one of those 2 is fine, and then do your finish work with good body filler like Evercoat Rage Gold.