Diverter repaired in shower

I need to have a diverter repaired in my unit next week in Belltown, Seattle. This is the shower unit. The external fixtures were replaced when the bathroom was updated several years ago. I believe it's the cartridges that need to be replaced, but not 100% certain. This is the feedback I had when a handyman was out to repair a few other issues Multiple tests showed different results. The first went to 108 immediately, but the follow up test was less than 95 degrees and would not rise. I can feel the parts grinding gently. It may be just old.