Just remove all the old silicone with a razor blade and clean the area throughly with alcohol. I like to mask off on both sides of the joint, about 3/8 out, with blue masking tape. Apply a bead of silicone and smooth with a wet finger. Let dry 24 hrs. Gently remove the tape. If it starts to pull the silicone, cut along the edge of the tape with a razor blade. Fill with water and check for leaks. Pretty easy.