Beeman Beeman 1783 "Siler Bear".

Hello!

I recently picked up a couple of Beeman/Marksman break barrel rifles at an estate sale. One of them is a 1783 "Silver Bear". It seems to be working properly with the exception of this seal crumbling. I have to assume this is the "breech seal", as it does NOT have the traditional o-ring style on the barrel breech.
I'm hoping someone can point me in the right direction on this one. All the usual sources seem to come up empty.

Thanks!

BSB1783B.jpg


BSB1783A.jpg
 

if you can get the old one out intact enough to get some meaurements, you might be able to fab one up from leather.