I guess my first question is are the markings original?
Don't think so, they look like something a repair person might make.
FWIW, mine has markings inside the cases just like cycle rangers, and those are original.
Do I stop all cleaning the bike to preserve the originality?
Don't fret about it. Make it nice. Ride it a bit, when you want. Patina is nice, rust dirt dents not nice. Can your PDR guy do anything with the fender? Mine has a couple dings from extended garage storage.
Do I dare ponder selling?
Not unless you lose interest or need it gone or need the dough desperately. I was fortunate I always had a place in the garage for mine and never needed the $500 a dusty and faded K1 might have brought in 1985. Yours is nicer but will the $5000(??) it brings pay for a year at Wisconsin?
I like the idea of a crate..... with hinges for easy in and out.