Had a valley start leaking and had several people besides myself look at it and no one see’s anything wrong. It’s a closed valley and 50 year shingles – shouldn’t be having this problem. I bought a bag of matching granuals and tared and granualed the valley with no luck. I was looking online and came across this stuff called Thru The Roof. It had over 200 good reviews. I ordered two gallons and brushed it on. It’s totally clear so it doesn’t look bad. It fixed it!