Measure the base of the chimney to determine how much metal flashing is needed.
With the measurements in hand, cut the metal flashing pieces to size using tin snips.
Cut 45-degree grades at the end of each piece of flashing. This will ensure that the flashing doesn't hit the roof when the sides are folded up.
Once the pieces are in place, use the hammer drill with the masonry bit attached to drill through the flashing and stucco. Set the drill to a lower speed to avoid shearing off the head of the screw.
Once the flashing is screwed in place, apply a dab of caulk to each of the screw heads.
Fill the entire reservoir on top of the flashing with sealant.
Repeat the procedure on both sides of the chimney.
Fill any other gaps between the wood trim and stucco to further prevent water from entering the home.