That was my plan but after disassembly, I discovered that the valve at the bottom was entirely brass so I just gave it a serious cleaning and polish. The rubber seal in the nut at the top was replaced.
I unscrewed the top handel portion from the pipe and the rod and main part of the valve came...
Just did mine after 15 years. It was getting pretty hard to operate. I polished alot of green oxidation off the brass rod at the top where the seal is. Greased it up with silicone dialectic grease. Well see at -35c latter in the winter.
I have had the same problem a longtime ago on a Massey 202. Inspect the camshaft gear closely while turning the crank to see if there is damage to the camshaft gear. Mine was a tired old machine so it was parted out. (Think it was a 4 cyl continental)