Can’t figure out how to remove cartridge of single handle tub faucet
The stem is held in place by a u-shaped piece of metal.  If you scrape through enough crud, you'll find the bottom of it on the outside of the metal cylinder.  Pull it out with a pair of pliers.  https://www.youtube.com/watch?v=ZkZad_sHQkQ about 0:50 in is what I'm talking about.