I have a shower where water is leaking through the tiles on the wall, leaving puddles on the floor. There are visibile gaps from where the tile shrunk along the lowest row of tiles right above the bathtub. Do I need to remove the tile and then recaulk, or simply recaulk where there are visible gaps? Will general purpose caulk work or do you need a specific water-resistant type of caulk? Also some of the tile is black. Do I need to remove that, or should I caulk over it.

Remove any loose or moldy caulk, then re-do it with a tub & tile caulk like this.

The tub and tile caulk Rick refers to can be purchased at your local hardware store under the name, Dap White Tub and Tile Caulk. Good luck, Tom