Firstly check you have the correct union nut at the bottom of carb body. There are 2-3 different lengths to those. Just above this nut is a bleed hole in the carb body and no amount of new gaskets will stop it leaking if the float level is too high or the float needle is not sealing.
A good first indication is to remove the float bowl and clean/blow it out, reassemble it, turn it upside down and try and blow through the petrol inlet. You can also prove it by operating the tickler to allow you to breath past the needle valve. You can also refit the bowl without the cap and watch the level rise and shut the fuel off.
If your float and needle are in good condition, but fuel is still seeping from the bleed hole, them maybe the float level is too high. You can try adding an extra fibre washer between bowl and carb to drop the level a touch.
On the other hand, these pre monoblocks will sometimes weep with just the tap turned on and then settle down when the bike is running. Ron