BS34's #3 carb bowl leaking

float is set correctly
needle and seat are sealing fine
i'm really stumped as to what is going on here
could it have something to do with the vacuum, this carb has vac line to petcock
fuel gasket isn't too bad but this isn't due to leaky gasket solely 
any help would be greatly appreciated  thanks 

How about checking the petcock?   Install a section of line onto both the fuel outlet and vacuum lines.  No fuel should flow out when the petcock is set to ON or RES.  Sometimes when the petcock fails, it sends fuel down the vacuum line.

thanks nes 

while searching the forum i'd read someone say they'd changed bowls and gasket which resolve the issue. 
so i followed suit and it seems to have corrected the problem for now. thanx all