I would recommend anyone that has gutter extensions to carefully inspect the seals around them. After pulling mine off I could not believe there was nothing behind them. You could see right down the backside of the drip edge with the rubber roof folded over the side, and the screw hole where water was seeping in.
Was contemplating not using the cover this winter because I am sure it was the cause of pulling the extensions away from the oem sealant. Then my wife said I'll get icicles pulling on them then. Guess it's just another item to add to the check list!
Pressure testing is the only sure way of finding these sneaky leaks.