Leaky Valley Shower

I have a valley tub/shower faucet with a pressure balance cartridge. When turned off it continually leaked past the valve and out through the tub spout. I disassembled the unit for cleaning and inspecting; everything looked great. Reassembled the unit but the problem remained. Purchased a new cartridge - for way too much. This didn’t solve the problem. What is my problem and what should I try next?

I never saw the Valley pressure balanced unit, but on the regular Valley cartridges it used the rubber cup seats and springs; these are the cause of drips. I would look under where the cartridge sits in the body and see if there are some little rubber cups down there.