My wife still brings up the garage sale flour kit at dinner parties like I discovered fire or something, so you are not alone in the weird science club. The iodine thing has been around forever but nobody talks about it because it is not as fun as blaming your starter for everything. I did the same test last winter and found out my cheap store flour was the problem the whole time, which made me feel real smart after two years of cursing my own hands. Stone ground stuff from a local mill is a whole different ballgame since the grain has more of the good stuff left in it. Old bakers knew what they were doing long before we had ten hour YouTube videos explaining why we failed.

Pulling the mirror box is the part people skip too. On a K1000 it's like six screws and the whole cage lifts right out, then you can actually see what you're doing instead of fishing a swab around the mirror at a bad angle. Naphtha on a brush gets the old grease out of the corners just fine, and the swabs finish it off. The trick is not flooding it, because if you soak the whole box you push grit into the shutter and then you're pulling that apart too. So yeah, if you're gonna hand clean it, pull it first, clean it dry on the bench, then re-lube the spots that need it. The tank just does the same thing with less control over where the crud goes.