The tub faucet is FIXED... (insert appropriate cheers from the crowd) The cost... a mere $3.14 . No plumber needed. After all of my internet research, husband and I decided it was definitely a DIY project. So we removed the faucet cartridge and found that the little black rubber o-rings/seats were slightly damaged. A trip to Home Depot and a little figeting with the screws and all was better. The problem was much more simple than we had imagined.
Still have the green stain though... gonna try the CLR tonight.