Grout is not going to be water tight no matter what you do. You are correct in your thought that water will penetrate. Do you know if there was a waterproofing membrane of any type installed behind the tile? If so then I would recommend fixing the cracks with grout and re-sealing. If not, then that may be a whole other subject and the caulking and grout sealer on the existing may be your best hope of slowing the water down. Caulking will certainly work and if you're happy with the look then I say use it. You will not trap the water as it will weep down the wall, through the corner, and under the floor tile as it would have if your grout hadn't already been cracked. I hope this makes sense and helps you with your decision. Please let me know if I can be of further assistance. Thanks for using JA!
thanks. yes the guy that put it in put in a pan and painted everything w some red membrane stuff. i would prefer to do nothing since its low on the floor and not so noticable. so you really think i can just leave it?
i know you said not watertight no matter what but i figure much more water would get in at any cracks in the corners.
Yes, the Redguard membrane you have works well. You should be fine. Take care.