Agree with those who said the problem is drainage. Water is collecting in your track faster than it empties. This is either from blocked holes in the track, water flowing outside toward your home creating an external ponding that is higher than your drain holes, or possibly your roof alignment is dumping a huge amount of water down the outside of the window overwhelming the ability to empty.
Is it possible the cement ledge on which your sliders sit is slanted inward? Seems unlikely but worth checking.
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Men plug the dikes of their most needed beliefs with whatever mud they can find. - Clifford Geertz
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