Hi,
I'm faced with lots of water in the passenger seat of my 1996 lexus es300 everytime there's lots of rainfall. I'm guessing that some drain is plugged with leaves or something but I really don't know how to begin to fix. Can anyone please help?

 

Last two vehicles I fixed with this problem (a Lincoln and a Honda), it was leaking from the covering fascia at the firewall/engine. Solution was to remove the wiper blades, pull the plastic fascia up, and re-seal it with some black silicone sealant.

I don't have your model so don't know if it's common on the 3es, but that's usually the cause. If there is a drip pan under the condensor that was plugged, the water spilling out would be independent from rainfall - so I doubt that's it.