I had a fuel valve leaking at the threads. It was made in Tailand, got it from J&P # 1257514. I used your O-ring idea, but no silicone sealant on the threads of the nut. I did use 3M silicone paste on the O-ring to prevent twisting damage to it. All good! Thanks

Mate you need to realise the rubber flat washer fits properly into a groove half way down the banjo nut