well I figured it out.
1) shut off the water (this is very important, ask me how I know)
2) remove chrome cover on center of shower knob
3) remove screw under cover, this allows you to remove the knob
4) remove 2 screws on larger chrome cover plate, this allows you to remove the cover plate
5) remove round split collar that goes around shower valve, it just pulls out
6) remove retainer clip. You will have to pull or pry this out the side. It should be oriented to where the clip pulls out toward the road side of the AS.
7) The shower valve cartridge should be free now. Grab the stem of the cartridge (where the knob attaches) and pull up. If it is like mine you will have to grab it will a pair of pliers and rotate the entire cartridge while pulling up. AGAIN I must emphasize, make sure the water is off before you pull this out!
Go to local hardware store and buy a replacement Moen cartridge, part number 1225. At my local Menards it was $20. I'm sure you could get it cheaper online.
Installation is same as removal, just in reverse.
Also, the faucet uses the exact same cartridge, and the knobs, and other small parts are also available if you need them.