There is a 7/8" hex plug located on the front & back of the pump housing. The rear one has had some seepage since new, but recently has begun leaking more. It appears that the plug is for access to a check valve & probably uses an o-ring for the seal. Curious if any others have replaced the o-ring & know what size it is so I can have one on hand when I remove the plug. I checked with Equalizer & was told they buy the pump & cannot provide any parts or further information.