shower stall leaks around the chaulking and onto the walls causing mould in the corners?

Answer 1

The old caulk has got to go. A flat-blade scraper with a razor-sharp blade will usually get it out pretty quick, but you need to work until all the material is gone. Any mold needs to be sprayed down with a 50% dilution of bleach. Next, clean the areas to be resealed with mineral spirits to create a nice molecular bond. The caulk I like to use in the shower is Pro-Series Quad white urethane caulk, available for $4.25 a tube at Lowe's.

After the joints to be sealed are clean and bone-dry, run a nice bead of the urethane caulk with a caulking gun, and work it in with your finger for a good seal. This will require mineral spirits for clean-up(not a water-based product) If you take your time and do a nice job, this can be a lifetime application.