"He’d designed a final drive chain that ran in a sealed enclosure"
My other bike is a Jawa 350. This has an enclosed chain, runs in rubber gaitors. They work really well.
Does anyone remember the the tins of chain grease which you put on the stove till the grease melted, then you put your chain into the tin? Before the grease had time to solidify, the chain was removed and left hanging over the tin until the excess grease ran off, and you refitted the chain.