At minimum, you should drill weep holes in the cans to allow standing water to drain. If you are ambitious, remove them. The globs of tar you see at the lower edges were used to waterproof the fasteners that attach it to the roof. Scrape off the tar and remove the fasteners. Patch the fastener holes with roof tar. Remove the entire flashing, tuck the up-slope edge of the flashing under a course of asphalt shingle, apply roof tar under the flashing at the fastener hole locations. Fasten down then tar over the fastener heads again.
A manufactured version of the same style of mount is pictured below, note the weep hole.