The gasket on my 18-year-old, large, Egg was recently replaced at the same time as the hinge was being replaced.
This material works very well, is easy to apply, and ,so far (several weeks), seems to be durable.
A few notes about installation:
1. It would be very difficult to replace the gasket without removing the upper shell from the Egg. If you are doing a hinge replacement, also do the gasket.
2. Clean the surfaces to which the gasket will be bonded as well as possible. A putty knife with the edge sharpened works very well. A little solvent, acetone, also helps. A propane torch, used with restraint, will help loosen the old gasket material. One should not use a solvent and a torch together!!
3..Following installation, a low temperature, 250F, was started and let burn for three or four hours. The low-temp fire aids in curing the contact adhesive on the gasket material. In several weeks of use, and a couple of runs to 700F, this material has shown no tendency to loosen or fail in any way.
4. If the gasket on your Egg is leaking, inspect the situation well to be certain that the Egg is not also suffering from a hinge failure. A new gasket will not correct, at least for long, a problem of misfit between the shells that is being caused by a failing hinge.