I put some gas in the tank and ran the engine a few minutes.
Then I discovered a leak at the reserve tank valve.
The valve is made by Ewarts on Patent. No. 344222.
Notice there are two tiny setscrews to remove before it all comes apart.
The rubber seals are hard, the obvious cause of the leak.
They are 3/8" long, probably originally about 3/8" OD to seal in a 23/64" bore in the valve body, and have a brass tube inside 5/32" OD x 3/8" long.
So what have others done about this valve?
Does anyone sell the seals?