Just as you had thought of doing.
Rain water running behind gutters.
If the gutters are clogged it s possible that the water is overflowing the gutters and this is contributing to the leak.
If the gutters look clear run a hose and fill the gutters with water.
When the roof shingles do not extend past the metal drip edge the water will suck back on the metal drip edge this is called capillary action and run behind your gutters.
The purpose of this product is to prevent water from running behind the gutter.
The first cause is when the roofing material is installed many roofers will not extend the roofing material past the roof edging or drip edge.
This product is an easy and inexpensive fix.
Capillary action is a water activity in which water adheres to a surface and follow the surface around.
Unfortunately this is a very common issue with rain gutters resulting in damage to the roof s edge as well as the structure s foundation.
If you have rain water running behind your gutters then it is likely that you have clogged gutters.
The exopsed part is not long enough about 1 long for the gutters to tuck under and can create problems with water running behind gutters.
Water should run out the downspout and away from the house without filling the gutter.
If this is the problem a simple solution is to slip some trim coil or sheet metal up under the d edge and flash it over your gutter.