you did replace the seats?
are you sure you got the right replacement?
did you by chance scratch the seat when installing?
Is the stem going into the seat a washer? A rubber washer? Did you replace that. Did you screw the screw down tight enough for the screw to compress the rubber washer?
Did you screw the stem back in place hard enough?
Therefore, pure speculation, but I think that you got the wrong size seat. There are about 50 different sizes and being off one bit can cause this. Or, you nicked the seat in install and the water is exiting there.