My bathtub has two handles - one controlling 'hot' and one controlling 'cold'. Lately, I've had a difficult time turning the water off because the handles are now able to spin completely around (previously, they would stop at the proper point and turn off the water).

I removed the handles and see a blue recessed cylinder that allows me to turn the water on and off (vs using the handles). The blue cylinders appear slightly cracked. My research tells me the fixture might be a Moen - not really sure how I can tell.

Question - what needs to be replaced? Is it the handles, since they keep spinning? ? The blue cylinders (are these cartridges? Stems?) Any advice would be greatly appreciated.