Gas cap refurbishment

My 741 has a very nice original oil cap with a perfect seal. One gas cap was missing, other was partially loose in its' center. I had a pair of good fitting gas caps, not quite original but well usable. The seals were like cardboard and were quite ineffective. I hand cut new seals from thin rubberized cork sheet. Fit is good.

Update: These seals failed because they ripped. Studying a Chemical Resistant Rubber Chart it suggests Nitrile or Viton. Will visit a rubber supply shop on my next trip to town.

I found the right place and they cut seals on the spot from 1.5mm Viton. I put grease to help them slide nicely. As grease will simply wash away with petrol/gasoline I want to experiment with silicone or Teflon grease. Already I tried CPU heatsink grease and Wurth silicone spray grease. Both seemed to dissolve too easily.
8Dec update: These Viton seals worked a treat so far with part tanks of fuel.. Not a single drop of fuel leaked. I filled the tanks and I can say this is the best the caps have ever been,

I want to uncrimp the original gas cap, remove the worn/loose center then attempt to recenter it with parts from a donor cap. It will be the first time I've done this so we'll see. The cap is not usable otherwise.

3Dec2018 Update: I gutted out the original cap. Firstly I tried to roll the crimp back but cap was difficult to hold. I made a tool for the lathe toolpost which utilized a hardened steel roller. I had some but limited success. Eventually I elected to machine away the internal part till it was wafer thin. Then it crumbled away leaving the outer case perfect.

DIY Lathe tool with crimp roller.

 Original gas cap dismantled

Another view 

Updates to come..