250.12 Clean Surfaces.
Nonconductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded shall be removed from threads and other contact surfaces to ensure good electrical continuity or be connected by means of fittings designed so as to make such removal unnecessary.
I think that is pretty clear that paint needs to be removed.... Outdoor grey painted panels will have paint also in any hole for grounding or bonding meathod. Short of re-painting the surface, after contact is made,(which I think is a bad idea... see 110.12(C)) something like NOAL-OX, Zinc paste or the stuff I posted a picture of to protect against corrosion on the electrical connection is required,
depending on environment. IMO If in an indoor panel, I think its a non-issue... Outdoor panel in salt air, different story.
110.12(C) Integrity of Electrical Equipment and Connections. Internal parts of electrical equipment, including busbars, wiring terminals, insulators, and other surfaces, shall not be damaged or contaminated by foreign materials such as paint, plaster, cleaners, abrasives, or corrosive residues. There shall be no damaged parts that may adversely affect safe operation or mechanical strength of the equipment such as parts that are broken; bent; cut; or deteriorated by corrosion, chemical action, or overheating.
Either way, I think a treaded connection in a thin can for a large lug w/ a large conductor like a bonding jumper is not mechanically strong enough for the purpose. And personally tend not to even trust the connection provided with panels connected by a 10/32. I don't know my own strength and tend to over-torque them...
