Incidentally, the leak is a small steady stream of gas.

I'm not sure if the small hole is an air vent for the float chamber, or a manufacturing defect. You likely have a float valve that is stuck open, or possibly the float itself is stuck. If the float chamber overfills, then gas will run out the hole. Since this is a new problem for you, the float valve must have been working OK previously. Have you ever taken a carburetor apart?

Before you tear down the carb, try this. Tip the bucket up 6 inches and drop it a couple of times. That will re-set a stuck float. If that doesnt fix it, tear down the carb.

It's a vent for the bowl. Thinking about how the leak started, I'd suspect some dirt in the seat, preventing the needle from seating.

Check the oil for gas contamination too.

I had a leak from that vent when i wasn't paying attention when i rebuilt my carb. i put the needle seat in upside down. Chances are you have corrosion buildup at the needle and seat and the needle won't close properly. causing fuel to keep coming. It has to leak out somewhere

Thanks for the replies everyone. It turns out my float was not floating due to a crack at a brazed joint. Replaced the float and I'm back in business.