The original coating was asphalt. According to the '68 Pontiac Sales Manual page Q3; "The inner fender, or shield, designed to utilize wheel splash to rinse away dirt, mud and salt, is protected against corrosion itself by a special coating of asphalt latex."

I used OEM Paints Underbody Preservatek asphalt-based coating to try to duplicate the original protection and look on a new well, a repaired well, and to freshen the other two. I believe it took three cans for the four wells. The bad news is the stuff is about $14 per spray can.

I would not remove any original that is in good shape.