NOS tailgate question

[oem4me]

After 50+ years being stashed in somebody's garage rafters, this turquoise beauty recently made it's way to mine. Clearly never used or retouched, this gate shows some crackling seam sealer above and below the center panel, which I've never seen before.
It occurs to me that every truck I've ever owned has come from a west coast plant (Los Angeles, or Fremont), so perhaps this is another Midwest or East assembly plant specific detail.
Who out there has an original gate that shows these beads of sealer, and where was your truck made? Any known original Fremont trucks have it?