I tried fixing a leaky bathroom sink faucet, just to find a completely different type of two piece plastic stem with the washer not screwed in, but having a little spring and cap type washer instead. I did not find which part was diffective (cold was tripping), so I just reversed all the parts and temporary shut off hot altogether. Are these types of faucets fixable? If so which part usually wears out, the spring or the rubber part? Turns out my whole bathroom has these types of stems. The cold water in the tub leaks from the knob every time the water is on (at least not continuously) This one also opens the opposite way (not lefty loosy righty tighty) and has hot and cold reversed. All I care about at this point though is to figure out how to repair plastic stems with springs.

 

Sounds like Delta ball-type faucets.
Do a Search above on Delta faucets, and you will find numerous posts on how to repair them (with bubble-pack parts kits made for the purpose).
If you have any questions after reviewing the Search posts, just come back on this same thread and ask.
Good Luck!
Mike