Oh wow, I'm doing exactly this right now! Almost exact same setup with a loose middle knob on a questionably old valve. I have access through the back and tile is still decent, so decided to replace the whole thing with a single handle and 3 to 1 hole cover plate.
vinegarstrokes420 t1_jab8rfa wrote
Reply to Shower valve versus handle replacement? by knewtoff
Oh wow, I'm doing exactly this right now! Almost exact same setup with a loose middle knob on a questionably old valve. I have access through the back and tile is still decent, so decided to replace the whole thing with a single handle and 3 to 1 hole cover plate.