Sealing the window exterior with silicone is a temporary solution, and not a very good one.
To get anything bonded again to where the silicone once bonded, will be difficult requiring strong solvents and elbow grease.
The fix is to remove window and clean area, treat the inevitable rust, and use new seals and compress them evenly. Then on exterior fill in gaps with a non silicone paintable caulk.
it is also possible the sliding window tracks are clogged so any rain that drips in the slider window floods over and spills inward.
It is also possible that the person who installed the windows penetrated this rain channel with the screws, so that it leaks past the screws.