My carb drools gasoline when at rest. It flows thru the intake manifold micro crack, and thru threads on the BTB / Man-A-Fre products plate that is under it. Gasoline can get thru most anything, not hermetically sealed, but, for all realistic purposes, I'd not worry about it. Carbs that have big issues with throttle slop are usually aluminum castings. My suspicion is in the airhorn where the idle cut solenoid is has a siphon effect. I have like three solenoids, two have different diameters, and four sets of O-Rings for it, and at least two O-rings are different in how they measure. I eventually bought a new OEM carb, still drools when the conditions are right, makes the header smell when I start-up. I need a proper repair on the manifold so the problem is out of sight, out of mind.
The identification of a vac leak at the throttle shaft will be a distinctive vertical line on the interior of the throttle body, but, the only ones that I'd imagine doing that would be the clone aluminum ones, as the cast iron ones are pretty tough, although I'm sure that there could be exceptions.