If it is the "new" "YF" I've seen, my opinion is it wouldn't be worth 400 pennies. As for the Zenith, CarbKing (the other Jon) needs to weigh in on that one. Who is this rebuilder are you talking to? No, in my experience this is not anything a common rebuilder would notice. They wouldn't take this much time at all and there are some people selling carburetor parts who I suspect might not even understand it if they saw it.
If the gasket between the float bowl and the throttle body is wet, there are only a couple of things that could be happening: 1. there is a crack in your float bowl letting fuel dribble down (would be rare but actually I've repaired such a problem in a YF before) 2. the "bonnet" is warped and that is letting fuel dribble into the recessed area below the diaphragm. From here, it runs through the drilled vacuum hole and into the throat of the throttle body and into the manifold as raw fuel. On the way down, it soaks into the gasket. Once the gasket has soaked up enough, it wicks the fuel to the outside of the carburetor. Nothing at all good can come of this internal warping. It happens because somebody over-tightens the "bonnet" pulling each of 4 corners down into the rubber of the diaphragm. And fortunately it is very easy to fix.
Please look at the very complicated tool I made. It is a 3 inch x 2 inch piece of nice flat poplar. I used a forstner bit (1 inch) to drill a shallow hole in it. Then I cut holes in two pieces of sandpaper...one 180 grit and one as I recall was 600 grit. I simply rotate the bonnet on top of the sandpaper until no low spots appear.
Hope this helps.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
