I've used that kit - works well. For a driver car like mine, I recommend using a 1/4" ball valve, Fixed for life.
Synchro, is your ball valve similar to the one pictured in post #11?
I agree it is not just methanol . I’ve replaced many valves doing service work and the repro valves are terrible. Have another one this week that hasn’t been in more than 3 months and it’s not shutting off fully. I wish someone would make a good valve. The ball valve you have shown in your photos shuts off fine I’ll bet.
Larry Shepard