Shower spout leaks when bathroom sink faucet is turned on or dishwasher runs. I replaced the two small o-rings as well as the larger one, but the problem still persists. This faucet is an older Kohler one handle, and has plastic parts. 4 screws hold the o-rings to the brass, but prior to the brass there is the plastic piece with the seats, the seats look ok? Is there any thing else I should be looking for?