After all these back-and-forth posts .... (sigh) if you had posted this picture first, you could have had your answer quickly. Here is a precise step-by-step pull and replace video to fix your shower. Notice he replaces his seats ... that is optional. His 4-way wrench is very trick but you might just rent one instead of buying one and never using it again.
Let us know how your repair went. (Yes, you can "Like" my post)