vaccuum leak?

Spraying the outside of the carb is mainly just for looks. If you do so, remove the choke pull-off diaphragm at the top or you will destroy the rubber diaphragm (if not already bad). The main use of carb cleaner is to spray down the throat to clean the throttle plates, and maybe clean the fuel outlets into the throat a bit. A rebuild is much better and more useful.

I would look for a good new or rebuilt carb first. For my 273, I got a new 2-barrel carb off ebay for $25. I recall seeing Holley 1920's occasionally, plus you might be able to use a later model for the Slant Six. Might also consider the Holley Economaster from the late 1970's. They made one for many carb applications for better mileage.