Like these:

http://teaguecustommarine.com/index....eal-black.html

http://www.ebay.com/itm/Silicone-Rub...item2ec3f60834 you can use a yard stick with a nail in 1 end and a razor knife stuck in it to cut perfect cicrles.

That Ebay piece says flame retardant. I don't think it can handle the heat of headers. Try Grainger or Mcmaster Carr. Most likely you will have to make your own or try and call the header manufacturer if you know who that is ???

silicone sheets handle the heat and stretch over the pipe for a tight flexible seal. i would use 1/8" thickness.(the ebay ad was 1/4 and just an example)and it is very easy to make you own.

CP is cheaper than EGay ..wow


http://www.cpperformance.com/p-16786...-material.aspx

http://www.mcmaster.com/#catalog/119/3528/=lvsj01

easy circle cutting

I have been making my own gaskets for years with a set of punches. That is a bad ass way to cut a big circle.

Should not be hot at the transom.

I made mine out of a semi truck tire innertube. Truck tire shops have them laying in the scrap pile and will gladly give you one.

I think your exhaust is 5'' O.D.? You'll want to cut the hole smaller than 5'', so it stretches over the pipe and fits snug and somewhat water tight.