I have a leaking shower. The shower value is one of these all-in-one valves, with one handle for hot and cold. It's about 10 years old. I actually have a replacement valve (pictured). Do these need to be completely replaced (brass assembly and all)? Or can I pull just the plastic and rubber parts out and replace them? If so how do you remove them? I see there's a C-shaped pin that comes out, but this thing is really in there good. How do you pull these out? Do they need to be unscrewed? Clockwise or counterclockwise when looking straight at it?