I use Turbo Poly Seal to seal cracked shingles. When a shingle roof butts up to a flat roof, then a leak can easily come from the shingle roof. Shingle roofs don’t last as long as rubber roofs.
Always check for issues on a shingle roof when you notice a leak appear under a flat roof. Skylights and vent pipes on shingle roofs are one of the main objects that would cause leaks.
We use Turbo Poly Seal from https://bergstromm.com/ to make all our repairs. This product stays flexible and can be used on any surface or product.
We use it to make vent flashing, roof drain repairs, skylight repairs, and metal roof repairs.
Waterproofing and Leak Specialists