I also have a 2003 Sable with this same problem. Like you, mine didn’t start leaking until well after the warranty expired. From what I have been able to find out the problem isn’t your a/c drain line. The water is coming from somewhere around the cowl and leaking on the inside of the firewall, into the blower motor, and down under the carpet. There is a Technical Service Bulletin(TSB) from Ford dealing with this problem. But if you take it to the dealership, they will fix it but you will have to pay for everything. With parts and labor, including a new blower motor because the one I had was rusting very badly beacause of the leak, was close to $400. I got with the manager of the service department and bought all the parts I needed and did everything that the TSB called out to fix the problem. Needless to say the car still leaks when it rains. I am going to try a couple of different things and will let you know if they work.
know how i solved this problem? i traded the car in.
i did not want to deal with that whole water-leaking problem & all that’s associated with it. i was more than a little pissed off that ford refused to do anything about it in my case, so i told them i would never be buying another ford vehicle.
i bought a honda instead. good riddance to ford.