I've got one of those (collecting dust), but there is no gasket for the lid to the collection cup. Pretty much there is an inset portion of the lid that the foam makes contact with and then drips into the cup. The only problem I've had with leaks is the gasket where the collection cup/riser tube meets the skimmer body, if that is not square and fully seated it will leak like crazy.

If it's truly leading from the lid then you will need to increase the amount of air into the venturi to lower the water level in the riser tube, that should give you a drier foam.

BTW if you try to completely seal the lid to the collection cup you will end up with problems, it is loose fitting so that air can escape, otherwise you will build positive pressure in the cup.

Hope this helps...