Sliding doors have seal at bottom, also look at track where it attached to floor, it maybe leaking under it between floor and track, look for cracks where wall meets the foundation, water could be leaking in or wicking in from crack especially if you got stucco siding? I suspect hard rain running down sliding glass and leaking in from deteriorated seal especially it the CYV 10 plus years old? Water not pudding in front of the door? If so it may be wicking in from crack below water line?
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