Holes, tears. Solder on a patch. See
copper. For safety, use a soldering iron rather than a blowtorch.
Chimney flashing buckled or loose. Force together seams that have come apart, and solder. If metal has pulled loose from the mortar joints or if mortar has crumbled away around the metal, rake out the joints, wet with water and pack in mortar of 1 part cement and 2 parts sand.