[jacquesm]

> Some places even drill additional holes thru virgin metal to access hidden areas, which damages the finish and exposes unprotected areas.

That's an exceptionally bad idea for another reason: cabling is often sandwiched in between two layers of sheetmetal to protect the loom from mechanical damage. If you start drilling holes in box members there is a fair chance that you'll end up doing damage to whatever is enclosed. And of course the debris from the drill is an excellent way to start the oxidization process.