Good observations. Long Branch receivers are generally very accurately machined. No doubt it was not found necessary to machine a flat for the pad. The residue around the area could be anything, including an attempt by Bubba to re-attach the pad at some point. I doubt anything like epoxy was used at LB as it would have needed to be removed before soldering.
Whoever gets it should dig hard to find that front pad. Might still be in Bubba's basement somewhere. Let's hope he put it in the butt trap!