Parco-Lubrite is just a TM owned by Parker Rust-Proof of Cleveland.
Lubrite is a manganese based coating. Requires more than just a tea kettle to apply. Needs a bunch of nasty chemicals and the tubs with precise temperature controls, etc. to hold 'em.
Zinc based solutions should give shades of grey depending on the metal it goes on. Manganese gives black. Go with the Radocy or Arma-coat. Caswell sells the kits too.
Did my .243 long, long ago. Hasn't had any issues of any kind since. The bore got done too(didn't have a small enough cast bullet to plug the muzzle.). No issues with that either.