I would venture to say that if the sheet metal were in need of a re-paint, it was not to cover up anything. I repaint every single one that leaves here. I do understand your concern, however if before and after pics are included, that is fine by me. Axeman-Anderson never used to paint anything, and you got 2 cans of Aluminum paint. DONE. Now some 60 years later, they do come painted.
The point being that a pressure relief valve that dripped for 30 years makes things look horrible, but functionally, they are just fine. The 'Bug Bomb' tune-up is NOT a rehab, however if the proper steps were/are taken, then there is no issue IMO. Witness the AA 260 that Keving did in Maine, or the fine Yellow Flame that Don has just brought back form the dead.
I do know something about this K-6 and the seller does very good work and is not in it to get rich. I have 2 machines running that came from his stable, and I had to do nothing to either one. Been a few years and only cleaning and lubrication. Most of the time you get what you pay for, and this is one of those cases.