1968 Plymouth B bodies were painted with the extension off, and the extension was painted separately, then bolted on. From the factory, the 68's used the black plastic gasket, which does virtually nothing to seal out water.
In 1969, the extensions were bolted to the car, sealed with seam sealer, then the whole car was painted. This was for several reasons.
1. simpler paint procedure. Fewer loose pieces to paint separately.
2. simpler assembly line procedure. less chance of mis alignment and paint chipping.
3. better weather sealing
4. better easthetics. makes the extension look more integrated.
This was a quality control improvement, plus saved time = money for Chrysler.
However decades later, 69's sometimes have rust in behind the tail light area because of the lack of primer and paint in this hidden area.
Remove a 68 extension and the nuts will be bare. Remove a 69 extension and the nuts will have body color paint overspray.
The seam sealer used was the same white latex based sealant seen on the drip rail, and other body seams.
