Orval Fairbairn wrote:
NOT ON ALUMINUM! The graphite from the #2 pencil will galvanically
corrode aluminum. Use a Sharpie and clean with either lacquer thinner or
denatured alcohol after you are done.

Why can't you just clean off the pencil marks?

Also, doesn't a galvanic reaction require an electrolyte between the
metals, so if you didn't erase or clean off the pencil mark but primed
and/or painted over the aluminum surface, no salt water or other
electrolyte could get in there to produce the galvanic reaction?