Not to be confused with the Diverter Cartridge. This cartridge turns the water on and off and adjusts the temperature.
Replace if water is dripping from the mixer knob.
Replace if water is dripping from the end of the spout. NOTE: not to be confused with water draining from the spout after the valve is closed.
4020 main valve
P4020 Mixer Cartridge
I grew up using dishmaster had my grandmother's house. So when I bought my house 35 years ago the first thing I did was install a dishmaster faucet and I've been using them ever since. Easy to get parts easy to service.
As earlier excellent expedient service. I haven't used them yet because I want to have them on the shelf at home if and when I get problems with the old ones.