volume and mute buttons did not work. After initial openning of iPhone, the ribbon control cable was severed.
When iFixit says a repair is "Difficult" they are serious. Be sure to have the iFixit Pro tool kit for these type of repairs. If I hadn't ordered it with my replacement part I don't think I could have made the repair.
I almost damaged the antenna cable that attaches at the bottom of system board. When putting any part back on make sure it "fits right". If something seems "off", then it probably is. So go over everything to make sure you haven't missed something.