Gerry, the original fuzzy door seals were done with a 45 degree mitre at the upper rear corner of the window opening. There was a small L shaped piece of flat metal that was slipped into both ends to hold them together. It was about 1 1/2 inches along each leg and maybe 3/8 inch wide, made of fairly thin sheet metal. I did not use this piece after replacing my seals and have not noticed any problem.
Now, the real trick is that fuzzy window seals for your rear vent windows are NOT available anywhere. What I did was to carefully remove the old seals from the metal rim, peel off the rubber part of the seal, remove the remains of the fuzzy cloth, glue on black velour, reglue on the rubber strip, and reinstall. Looks original. Some fairly bad pix of how I did it on my web site http://members.home.com/ehubbard5/ then click MGB GT and you will find it.