Using gutter sealant is an effective way to treat leaking galvanized steel and aluminum gutters and downspouts. It is very sticky, so try to avoid contact. Problems with copper gutters are not as common and can be corrected by re-soldering where necessary. You should clean your gutters and downspouts twice a year, in the spring and fall. Use a garden hose to flush out and clean the gutter.
The gutters should be dry or the sealant won’t adhere. It also will not work if the air temperature is very cold. Areas to check are the joints, end caps, outlet tubes and miters. All should be pop riveted; if not then rivet. Apply sealant liberally to all those areas. In galvanized gutters check for any holes or cracks where rust has occurred and seal. For larger areas make a metal patch and adhere with sealant. Check the pitch of the gutter with a level. It should be ¼ of an inch for every 10 feet.
Debris can get clogged in elbows in downspouts. Flush with the hose and let dry. Take the downspouts down and take the elbows apart. Use gutter sealant around the pipe that fits into the elbow and pop rivet, then re-install.