I wish I had a sample of the original, no matter what condition. Then I could create a correct replica. Even a photograph would help. Failing that, I'll do as Benicia suggests and trace around the handle housing. I'll probably do a 2D Cad drawing of the result so at least my version of this gasket will be on file to share. I imagine there will be a lip (recess) on the original around the inside of the handle casing. If an original one comes to light I'll measure it and then perhaps one of you kind 3D experts can create a file for future use.
Thanks to everyone for the input.
Rob