carb leaking, and running rich

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I had the feeling my '72s 350 with stock carb, was running rich, at least when idling--starts easily, runs better the colder the weather, restarts require pedal to the floor, when warm, idle gets progressively worse then dies--but to be sure used a colortune to check it.

When I removed the air filter I've found that with the truck running, there is a hint of fuel leaking from the base towards the front of the left side of the carb, near a horizontal screw (throttle stop?). When I shut the truck off, it leaks considerably more, soaking much of the left base of the carb.

Is this likely to be just a gasket --I'll confess I did remove the carb and clean it/check float, etc. a year or two ago WITHOUT replacing the gasket? I've read about leaking fuel wells--can they do this? Or are there other possibilities I've not thought of?

I'd appreciate any thoughts you might have, before I start taking things apart! Thanks.