As long as it seals air-tight, I'll think you'll be very pleased with the results.
I used liquid silicone gasket for 2 different Columbia Viva-Tonal #16 reproducers, since there is no modern replacement available, you have to make your own.
And I was very pleased. Not only did it seal very tight, it also is very soft, but still stable enough to hold the reproducer firmly.
Liquid gasket is available at auto-parts stores, bicycle shops & of course online, even at eBay.
It comes both in clear & white & I've also seen in red & black color.
I am in no way an expert nor an engineer, but to my layman brain, it makes good sense to have a flange that is a soft as possible, without compromising stability ofcourse.
It should allow the reproducer to track freely & also a softer material, but still kind of sticky, like soft silicone, should make for an excellent air-tight seal.
If one would have the time & some spare brass inserts for reproducers, it would be great fun to make a mold, perhaps out of silicone or latex & try out some different types of silicone & molding resins.
IIRC there was a discussion not that long a go at some of all the phonograph related board around, were someone wrote about a prototype flange they had gotten from someone who was trying to make flanges (I think it was for exhibitions, not sure.)
The maker gave it away, thinking it was a failure, since it was waaaaay to soft, compared to an original.
But, they writer stated that it was the best flange he had ever tried, just because it was so soft.