Folks,
Kali has the right idea!!
The form in place gaskets used in the automobile industry are based on silicones (....), which are amongst the most inert and heat resistant polymers known.
If you would like to get better hardness (shock resistance), add fibre glass (as in strands of fibre glass, not in the woven format) in the compound and mix it throughly and apply on the gas port. Also, if you would like to produce this in relatively large quantities, you could buy silicone gasket sheets and cut them to appropriate size.
Another way of doing this may be to use clear silicone caulks, (not the acrylic based caulks, which also dry clear) used in home construction industry, with added carbon or talcumm powder as filler, for making these gaskets. These are all air dry products, so it takes a while for them to cure. The curing process could be hastened by increased moisture in the vicinity (bathroom..), and give a very flexiable and heat resistant compound.
Good luck Kali...!!
-thepusher
PS: Please apply some release agent to the metal surface prior to appling either gasket material, as the removal may not always be easy. Very light coating of gun oil may do the trick.