Thermoquad fuel leak

In my experience, even on a stock smogger teen;
air leaking thru throttle-shaft bushings,
has never been an issue to me,on any carb;
even my 50 year old original-bushings TQ.
Well; with the possible exception of the carb on my ancient worn-out super low compression, early 80s LawnBoy lawnmower, which I finally retired several years ago...... but still have. It got a lil hard for my wife to pull-start.

Your results may vary.

Here's how you can tell if yours has a problem;
Set the transfer slot exposure underneath the throttle blades to a lil taller than wide. Close up the secondaries tight but not sticking. Reset the mixture screws to 2.5Turns from lightly seated. Make sure your float level is set right and pressure test the float valves. And prove the mainwells are NOT leaking . Install a new, correctly calibrated PCV valve.
Install the carb, start and warm up the engine. Then set the Idle-Timing to in the range of 8 to 14 degrees.
Now; what is your idle speed?
Depending on your cam, and it's install, it should be between 650 in neutral to not more than 800/850.
If it is more than 850@12degrees, then the engine is getting unregulated air from somewhere, not necessarily from the bushings. Search it out.
In your searching, you can spray chemicals onto the bushings to see how it affects the idle speed. Do not spray gasoline! I have used water, brakleen, propane, and CO2. Brakleen is cool cuz when it come out the tailpipe, it is highly irritating to your nose. Water will turn to steam. Only pay attention to the change in idle speed. I doubt your engine will even notice propane.
Now, if the bushing slop affects where your idle speed returns to, as in not the same every time, first make sure the the Transfer slot is adequately positioned. If you have set the Idle-Timing to some large number like 18 or 20 degrees, then your throttles will be very near to shutting off the transfers, and your Mixture screws will be doing all the work. So if the throttle does not return to the same place everytime, now you can blame the bushings. But after you install the new bushings, you will find that, if you have not backed off the timing, you are STILL gonna have problems with both the idle-quality, and the tip-in hesitations. So the take-away here is to be sure your transfer slots are contributing adequate fuel. Do NOT try to idle on the mixture screws; they need to be in the sweetspot of adjustability near 2.0 to 2.5 turns.
But everything depends on the correct wet fuel level; get that wrong and suddenly the carb gets a bad reputation. Get it right, and you will think you are driving an injected car.
Happy HotRodding