Result..... I decided to take the high road and just submerge the head in a bag of white vinegar taped around it. Funny but after I got it secured in place, the bag sprung a leak but with quick thinking, I got tape to stop it and it worked good enough. I left it submerged for about 9 hours. My wife used the shower after my repair and said it was noticeably better. In hindsight I should have taken the head off but I was so careful when I put it on with plumber's tape 6 months earlier, I didn't really want to disturb it so that was the reason I took the high road.