I've never seen anything else available for a Healey, like neoprene(sp?).
I get a pretty long service life out of my rocker cover gasket; I only adhere it to the (aluminum) cover, and don't have any trouble with it sticking to the clean and dry head flange.
I think the secret is that the head flange is scraped of paint and wiped of oil prior to assembly. Just a thin smear of silicone to stick the cork gasket to the aluminum or steel cover.