One of my riding buddies has an Ultra Classic that has a cast rear wheel. Here's his problem: Rear wheel has a slow leak that leaks down to about 20lbs. He can reinflate & it will hold for a couple weeks then it's down again. The set-up is tubeless, & he wants to keep it that way if possible. He's check the tire, & stem carefully... & he said it did the same with the last tire he had on the bike. I'm thinking there maybe a small pinhole in the casting of the wheel. Here's my question... Is there any type of sealing agent that can be applied on the inside of the wheel (Not Slime), but applied with the tire off, maybe with a brush applicator (Thin coat) that will harden ?