Most likely it will be a hydraulic, between the mating surfaces , of the two halves of the valve body...If it heated up, It might have warped.check it with a straightedge and also check the gasket for any tears.Also check the vaves and see if any of them bind when moved back and forth. The slightest binding can cause the problem... Like I said earlier , If you never did this before,I don't suggest it... If you drop something and don't know where it goes ... you know.