As many of us have this issue, I thought I would share what I used for Project Floyd. After a great deal of research, I decided on using this product: Evercoat FIB-822 Maxim OEM Bead Type Seam Sealer. It has a 5 minute work time (works like caulk or silicone) without running like so many other products. The other major bonus, while it is a two part product, no special caulking gun required! It fits right into a normal caulking gun and comes with two applicator tips. Can be top coated (painted) in 30 minutes. It is a little spendy, around $45 on Amazon.
Pretty simple to apply. I first chipped all the old sealant out (no holes fortunately). Then proceded to sand the entire gutter with 180 grit sand paper. Wash clean with acetone, allow to dry. Once dry, just apply it like you would caulk or silicone, filling the gutter with sealant and leveling with a finger (wear some latex type gloves).
