Corner leaks (aluminum)
Easiest way to tell if a gutter corner is leaking or not is to look at it shortly after a rain or a good shower. If the corner sealant has failed you will see dripping from that corner’s bottom.
And this way you can’t mix up the dripping with rain drops coming down the outside of the corner because the rain has stopped already.
Some other signs of corner leaks: mold/moss growing on the outside of the corner, drip marks on the ground directly underneath, blackened fascia board behind corner, paint peeling off fascia board behind corner.
Why repair corners?
If it’s not dripping on your head or creating a puddle then turning into ice in winter time why bother, right?
Wrong! You may or may not experience immediate inconvenience from a leaky corner, the real damage is done over time. When a corner’s sealant (caulking) has failed water and moisture will get behind it, to the wooden structure: fascia board or rafters (to which the gutter is attached to) will get rotten resulting in the gutter to detach despite proper fasteners in place; moisture will seep up to the rafters and further up into the roofing structure causing water damage there.
When this problem is left unattended for a prolonged period of time it will become more than mere gutter problem, it becomes carpentry and other water damage related issues which can turn into more extensive, and expensive, structural repairs.