MrT..........the float valve seat really hazzta be "honked-on". It leaks BEHIND the brass seat. Recommend you squander $2 (cheap) for a 1/2" FLAT blade drill and grind the POINTS-OFF so it will fit in the soft BRASS seat. Common 1/2" screwdrivers are "V"-shaped (wedge) and will NOT transmitt enuff torque to the soft brass seat before the slots are broken out. Iff'n yer really cheap, a short piece of broken hacksaw blade innna vise-grip will work.
And ALWAYS remember to turn yer glass under-the-tank fuel valve OFF after the days work is done. In the morning, 2-turns ON. I marked my round fuel valve wheel so I could count turns. ........fuelish Dell