I don't think any paint will withstand and fuel leaks. Any professional carb rebuilder or restoration company can replate all parts, rebuild and make that carb look like brand new. The only way I would go. The Carburator doctor in Camrose, Alberta if no one in your area. You can ship to him if packaged well. Rusty is the man! Use my name as a reference.
Agree with Ziggy on a professional rebuild, amazing what a competent rebuilder can do. Eastwood restoration products sells a carburetor paint in an aerosol can but silver is the only option.
an ultra sonic cleaning tank will make a carb look brand new without the use of any harsh chemicals. murray may remember one that i did for our late pal ray kyles.