I looked about 18 (?24) months ago and could not find one for my 1961 650 Standard. Eventually went for a solid copper one from RGM. It wasn't my preference but has been good. No leaks of liquid or gas, and am very happy with it. I did keep torquing it though, just as I would a composite one. Smear of 3-bond around tye pushrod tunnels may have helped
Andy