Spit works fine until you're on a boat where everyone's sharing a rinse bucket, then it's just gross. I watched a divemaster in Florida use a potato once, just cut it and rubbed it on the lens, swore by it. Never tried it myself but now I'm curious if the starch thing actually holds up.

Wrapping in butcher paper isn't really what caused that burn, it was the air left in the wrap. Paper alone will let a cut dry out and go gray in a couple months no matter how tight you think you got it. The fix is to press plastic wrap right against the meat first, then paper over that, which is basically what the sealer does in one step. Vacuum sealing is easier and lasts longer, but plenty of guys got by for decades with the plastic then paper trick.

Watched my buddy do the exact same thing last spring, ordered a 58mm filter for his 72mm lens and didn't notice until the box showed up. He grabbed a cheap step-up ring off Amazon for like 12 bucks and it worked fine, no weird blur or dark corners, just had to screw it on tight. So yeah, the ring fix is real, you just got unlucky with a bad one or maybe didn't seat it all the way.