Porthole rubbers first 456
First of all, it is fabricated by Goyot france.
Find a Goyot ditributer and ask for the rubber.
You cab buy it on bigger length so you just cut of what you need.
It is very easy to replace.
To cut out the old rubber which is a round rubber, use a small round spade to cut it fron the bottom.
The use a simple sealent like sikaflex and put very little in the frame.
Then bring in the rubber and make the connection on the highest point. Good luck.