Fighting the fouling problem, I packed the base pin of my Armi San Paolo 1858 Remington replica with a silicone grease used by SCUBA divers for o-ring seals, Zip-Slip brand. The stuff will sit atop molten lead without any noticeable effect. It worked pretty well but I cannot compare it to any other solution. I suspect that anything that will stay put, not flowing when warmed by the heat of firing, will do the job. Cleaning will be eased if the packing you choose surrenders quickly to the cleaning solvents you use.