Did the Factory Use Any Kind of Sealer on Fender Seams?
on my 67 there was remnants of an expanding foam type of sealer in the area you pointed to. I bought a section of the rear valance? ( between rear glass and trunk) and the same expanding foam like sealer was in that too where the pinch welds came together.
the 67-69 Dodge & Plymouth Body and Electrical Assembly Manual available from Faxon Auto Literature has the details. ( worth the money but a bit hard to decipher) shows spot welds and inner panel sealer, electrical wiring routing, decal placement etc