Like Joe said, each company has their own stuff, and each company has many different faucets. The offsets have to be exact, or they won't work. Your faucet has water coming in from each side mixing in the middle. The diverter is a valve just like the hot and cold. When it is open, by default the water flows down out of the spout (even under pressure, water follows gravity). When you close the diverter valve, the water flows out the top hole into the shower. For this to happen, the bottom hole must be closed off. The valve and stem both must be the right diameter and length, our it won't seal (why you still have water coming out of the spout). These dint normally have replaceable seats ... Those are usually machined into the body. If you know the model number of your faucet, Price Pfister can give you the part numbers you need. If not, you may just want to replace the whole faucet assembly.