Original installation squareness.
Anderson skylight window leaks.
Take a moment to seal any cracks you find on the cover with the clear silicon caulk.
Start by checking that the windows are basically square in the frame.
Leaks at skylights left unattended can lead to costly structural damage rotted roof sheathing rotted roof framing and wet moldy insulation as well.
At the time of installation 3 years ago our contractors had a anderson rep out to replace seals in 4 or 5 of our brand new skylights.
Sloped glazing such as roof skylights probably has historically had more leaks into the roof structure due to improper roof flashing than other window failure causes.
I also see water stains on the bottom of the wooden window frame suggesting there has been wind blown rain or snow melt leakage too.
I think your anderson slider window has more than air leaks.
Two years later after a downpour one of the other skylights developed a leak.
1 lift up the shingles next to the skylight one at a time and brush out any dirt and debris.
Unscrew the fasteners holding the cover of the skylight window on with an appropriately sized driver.
To fix a leaking skylight.
Then press down on the roofing shingles to seal them tight.
Then lift it off and keep it to one side.
Anderson rep said seal was defective.
They leaked brand new.
Our new anderson skylights leak.