Gutter leaks usually start at rusty spots or seams that have opened up because of expansion and contraction. If your gutter is still basically sound, the easiest way to stop the leak is by covering the damaged area with roof and gutter repair tape.
1. Prepare the gutter by scraping out as much old tar or caulk as possible. Clean the area around the leak with a stiff scraper and a wire brush, then rinse off all dust and wipe completely dry to give the tape a clean surface for bonding.
If the gutter is badly rusted or has been heavily coated with tar that you can’t scrape out, spray on a special adhesive primer before applying the tape.
2. Cut the gutter repair tape with a scissors or a razor knife long enough to overlap the leaky area by at least 6 in. in each direction.
3. Tear the paper backing off the tape and lightly adhere one edge of the tape to the top of the gutter. Starting at the center, press tape firmly into place. Follow the contours of the gutter and smooth out all the wrinkles and bubbles. Overlap long seams by at least 1 in. and end seams by 4 in.