ORIGINAL: jib
I ripped a mufler gasket recently and my local LHS didn't stock it, so I cleaned up the muffler with alcohol and pressed the mating surface into an ink pad, then I stamped a heavy sheet of paper about a dozen times with the mating surface imprint. A few minutes later, using a fairly new blade in a razor knife, I easily cut a nice paper gasket out and put the remaining paper in my engine file, so I had more gaskets ready to cut out for the future. Even the bolt holes are easy to cut with a razor knife.
This whole process took less than 15 minutes and did not involve gluing the muffler on with RTV, dealing with the ooze on the outside and potentially on the inside of the engine, hindering the exhasut flow to the muffler.
I used to cut 90% of my own gaskets for my old British cars and motorcycles, when they were hard to get or I couldn't afford to buy them. Now, it's just easier, faster and every bit as good.
Jack
Steve:
I have done the same, using a manila folder as gasket material; with excellent results.
I copy the track by putting the board over the surface previously oiled (not much, just wet).
I made the holes by punching with a brass tube over wood.
Even better results are possible by soaking the gasket in castor oil before installation, and re-tighten the bolts after a couple of flights.
If taking the silicone route, use the red staff for high temperature.
Regards!