The leak is before the fuel and air mix so the problem is the idle. The seal is only the attachment of the cleaner to the carb. I belive a rich mix compensated by a high idle to keep it running is spitting a little fuel back through the carb every once in a while, gravity pulls the fuel down throu the gap in the seal it will not cause any mixture change as it is before the fuel and air mixes.

If fuel is escaping then it is possible dust may get into the engine after the filter so make sure the air cleaner is strapped down air tight