Shower diverter turns but doesn't divert (v2)

I posted Shower diverter turns but doesn't divert a while back about a diverter that turns but won’t divert. Thanks to the community I learned some terminology and that I needed to open up the hole to get a wrench in there.

Well I used a dremel bit made for ceramic to open the whole enough to get a nice wide (1-9/32) wrench in there. And I turned and got this nut out

Behind the nut seems to be just a single piece. Is there something I can take out and replace here or do I need to remove the entire valve? (which screws in 4 ways and would require removing quite a bit of tile I think)

update: i’ve now lost the nut inside the wall :-(. i turned the water back on and it’s not leaking (yet?) so i guess that’s good…