There is a gasket but when i did mine the new gasket also leaked so removed it and used Loctite RTV sealant no more leaks.
https://www.cromwell.co.uk/shop/adhesives-and-sealants/gaskets-and-jointing/598-high-performance-rtv-silicone-gasket-maker-300ml/p/LOC7255378W
You can get it in smaller...