How do you find leaks on Dimensional Shingles???

Because there is no 'definitive nail pattern', as there is on normal 3-tab shingles....we sometimes find that the roofers have shot nails thru the shingles...and then the next shingle up does not cover the shingle...or that it is on the 'seam' of the shingle above.........and it seeps thru and leaks....

After investigating the dark spot in the attic from the roof leak...we 'tapped' on the nail until it lifted the shingle....and we went on the roof to locate the culprit....here it is....see the rust..?

you can see where they shot the nail too close to the 'lip' of the shingle....and the one above did not seal it enough..

we put our '$4.00 per tube' sealant (a Tripolymer that remains flexible) on the area after resetting the nail...

and then dipped it down to cover the nail...this way the shingle will not 'flap' when the rain hits....after lifting the old shingle, you can lose the factory seal...

and we sealed the ButtJoint where the 2 shingles meet