While I have not personlly used Master Gray, it sounds exactly like the various case bond materials used on motorcycles. The case bond is more like a cross between a glue and a silicone. (It isn't silicone based) The material is semi-hardening and more "digestible" according to the manufacturers than silicone. There are case bond marteials from Honda, Kawasaki, Suzuki, and Yamaha. I have used all of them. The best I have used is YAMABOND. I have had very good luck building oil tight engines with it. It is NOT intended for use on gaskets, only on clean flat surfaces preferably machined. Might be  way to find a workable material locally.