RCA 6T71 KCS47 question

[7"estatdef]

The .99c wonder is coming along, resently I was able to get a 16GP4 from a very nice list member. If you remember the original had a broken neck. Sawed off the bottom 4" of both sides of the cabinet as they where badly water damaged and have reconstucted those two areas with new wood. While I was doing the cabinet work I pull the chaiss and crt and was getting to install the new crt after cleaning the mask. I noticed that there is a black rubber gasket that was in the mask. It's in bad shape I was wondering where does it go? Around the front edge of the crt? Is it there to cushion the edge of the crt?
Tnx
Terry