Water accumulation behind driver's seat

1996 Olds Cutlass Supreme, 104,300 miles. A year ago, I noticed a lot of water on the floor behind the driver’s seat. Went to an online auto forum and read 1) problem with window, door seals etc. 2) problem with seals around windshield & wiper console, 3) problem with heater hose and/or coil. Took it to the mechanic I’ve been going to for several years, good guy. Ruled out any seal problem. Instead of tearing out the dash assembly to get to the heater hose/coil, he installed a by-pass between the A/C condensation drainage and heater hose. This worked - until a week ago. Now the water behind the driver’s seat is back with a vengeance. He wants to remove the windshield and wiper console and reseal the whole area. Before he suggested this, he removed the protective panel beneath the glove box on the passenger side and ran water through the wiper area. Sure enough, there was a noticeable trickle coming through – but on the passenger side. How does water get from there to behind the back seat without showing up anywhere else? Does removing the windshield etc. and resealing make sense to anybody out there? Appreciate any informed responses. thanks.

If this is a FWD car, then there may be no hump between the seats to prevent water trickling to the lowest point from the entry point. If you have a center console, the water may go underneath or bypass it under the front passenger seat.

If it was coming in from somewhere around the dashboard area, I’d think that you’d notice wet carpets up front. Could be it’s coming in from somewhere in back. That happened to me in my 10 year old Integra – there was a hole (I could never find) that let water in – I suppose – under the rear seat. You could hear it slosh back and forth on turns. One very wet day it overflowed into the rear footwells and fried the computer under the passenger seat. You may well have two separate leaks (wiper area on the right, and body hole on the left). I’ve never seen a car that didn’t have some center hump, so I doubt water is moving from side to side.

Does it have a sunroof. If so I would look for a blocked drain.