Check for leaks around the petcock - where it screws into the tank, where the fuel line connects to it and around the on/off/reserve lever. There are gaskets that can dry out and leak.
Check for leaks around the carbs - where the fuel line connects, around where the bowl fits to the carb and under the carb on top of the transmission. The inlet needle might not be seating and the bowls will drain out the overflow. It'll stop once the fuel level drops, but the fuel can pool on top of the transmission. It may have overflow tubes that snake down between the back of the trans and the swingarm, so check on the floor too.
Easiest way is to feel around with your finger and then do a sniff check to see if you're picking up fuel.