That horizontal seam was sealed with seam sealer at the factory. If you haven't painted yet, sandblasting along the seam and putting seal sealer there, pushed tightly into the joint would be your best approach, IMO.


Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.