This is what I remember form my issues from last summer - details may be foggy.
Synchro - If I remember what I was told correctly, the kit only works on an original Shutoff Valve, not on repop/replacements?
Nabebess1930 - I agree both should not seep overnight. Of the 2 the float bol vlave can be the hardest on to get to operate properly. with a Full tank you have 10-11 gallons of gas/pressure that the this little valve is trying to seal/stop. Replacement float bowl valves are also iffy on if they will work. I do not remember the exact details, but some repop styles the needle can be removed, and the needle/seat can be cleaned out. Reports suggest that the issue is they are not sufficiently cleaned of machining debris. Same for the Shutoff valve - debris scratches the ball and housing around the ball in the shutoff.
Here a just of a couple of previous treads on the subject. If you search you will find more.
https://www.fordbarn.com/forum/showt...=leaky+shutoff
https://www.fordbarn.com/forum/showthread.php?t=250572