MG T-ABC

I have one of the rubber gearbox covers on my TC (I think one of the Moss parts). it now has that "sticky" feel to it as it has aged. Any recommendations on how to treat the rubber?

Others may have better solutions, but I used to use vulcanizing compound to clean rubber back in my bike mechanic days. Specifically a product by Rema called Rubber Buffer. It looks like they still sell it under the name Liquid Buffer.

I used clean brake fluid to clean up mine, but it was an original cover and not a Moss one. After it was clean I coated it with Castrol Red Rubber Grease and then wiped off all the surface residue until it was clean and dry. Amazingly, the rubber is still supple. The rubber cover was supple before the cleaning, I will note.