If this is between two screws when your looking at the front of the pump then it is in the suction gasket between the pump pot and the pump housing and the one you have could be a paper gasket and should be replaced with a rubber or cork one this can be done by removeing all four screws and gently pulling the two pices away from each other and clearing the old one out and putting the new one in. That is the hard part as there will be a extention comeing from the pump into the pot and is about two inches long you need to clear this with the new gasket and then just put the screws back in and fill with water.
If your looking from the back of the pump and the leak is between the motor and seal plate of pump then it has a bad seal and will need to be replaced. For this you seperate the half's of the pump by takeing the band clamp off pulling the front from the back then remove the five screws on the defuser pull it off if there is a screw in the center of the impeller, that is left handed and unscrews by turning clockwise. then unscrew the impeller and replace the seal. Reassemble pump with new "O" rings and fill with water.