I have the same model carb that did much the same thing. These aren't listed in a particular order of testing, but a couple of things that might cause your leak:

Porosity in the carb casting, that fuel can leak through petcock casting underneath where the rubber seal contacts. You may be able to test for this by disassembling petcock, tape carb throat closed at both ends, and clamp carb in vise with petcock faced up, as perfectly horizontal & level as you can get it. Dribble a few drops of fuel in petcock reservoir and gently tape over the opening, or seal with a gasket material & weight on top, without disturbing the tiny puddle of fuel. Carefully peel off tape or seal & check it after a couple of hours & if fuel's all gone, casting is leaking.

The petcock's openings are like little barrels, and the outer rims or faces may not be perfectly true. Some stuff in some fuel is corrosive & can erode aluminum. This could prevent rubber seal from stopping fuel flow. If this is the case you can make up a little resurfacer tool to dress them flat with some valve grind compound or an abrasive paste made of fine emery paper sand & grease, or with a disc of fine emery on a home made dressing tool, removing as little material as possible. Might be best to dress by hand instead of a high speed power tool. Also clean out where the spring fits & dress metal surfaces so that the parts fit as tightly as possible by spring's pressure.

If it's neither of those problems, I believe the fuel inlet needle seat is removable on that carb so it might be leaking where seat fits into carb body. Fix is obvious, with a sealer used on new seat in case casting is helping to cause the leak.

Float level is designed to allow enough fuel in bowl to operate engine at all reasonable angles. A slightly lower fuel level would never be noticed. I would lower float level slightly to increase tension on float inlet needle.

Could be your fuel cap breather is nearly clogged, so that at running a slight vacuum develops, but not enough to stall engine. Then after sitting, atmospheric pressure returns, causing higher relative tank pressure, contributing to later leakage.

Lawnmower or small engine shops have some dandy little aluminum inline fuel shutoffs that will solve the problem by shutting off all fuel from tank to petcock.