I am trying to stop my bathtub faucet from dripping. It's a 3 knob design and the drip is coming from the cold valve. The valves and washers are new. The valve seat for the cold side is deeply pitted. The valve seats have a square hole in the middle. The internet tells me that they can be removed with a valve seat wrench. However there only seems to be one size of valve seat wrench and the smallest size on the wrench is too large for the hole. The valve seat wrench only accommodates 3 sizes. A google search has not found a smaller size wrench.

Are there other sizes of valve seat wrenches, or is it likely that these seats can't be removed? Unfortunately I don't have a brand name.

I have tried to resurface the valve seat but it still drips.

Thanks for any help you can provide.