I lapped mine and it never leaked. Did you check the float for leakage, submerged in a glass of water? How about the gasket behind the needle seat and the plastic bowl seal?
My petcock was leaking as the seal had dried up. I brought a few replacements but they werent exact. The valve was cheesy and seemed too small in diameter to turn smoothly. I took the valve out of the body and plugged the hole with an aluminum disk and gas-resist gasket. Plugged one passage, Installed a motion pro inline fuel valve.
Look out for aftermarket carb kits, the gaskets can be cut undersized and cause the float to snag, improper jet sizes, inferior materials that aren't gas-resist.