92-lesabre-water getting inside

just purchased used 92 lesabre
during heavy raod water conditiond I get water in car
once about 1/2 inch in rear passenger floor board
there is rust along top of floor pan near doors
all of the trim/carpet hold downs are rusted
the worst area has the most rust,
There is also some bracket and exhaust gaurd metal displacement underneath car like someone backed over a rock.
But with the rust along florrpan inside I'm guessing it is coming in arond the doors.
I cant firgure how that much water got in around doors??there is gap in whether strip/trim at the bootom (the stuff shrinks after time) but water would have to jump or capilerate about 1/2 inch to get over metal seam
May be coming in from top and running down inside of weather stripping?
Is this common to buicks (1992) I have a 90 Olds 88 and it has much better weatherstrip system (I even have 1/2 opening on outside from door dent and it doesn't leak a drop inside)
Anyone with similar problems??
Weatherstripping I can add or fix easily but alternate taking seat out and using interior seal coat sounds daunting, smelly, and painful.

The right way to do this is to take out the seats and carpets. You have to dry the carpets and padding or they will smell. Then get in the car while someone runs a hose over the car starting from the bottom up, one door at a time, then the front and rear glass. We had lots of these leaks on the early 92,93. It always happens on a changeover model year. The door gaskets leaked and the rear glass too. Check the sunroof too, the drains run down 4 corners from the roof. Check for water coming under the dash from the evaporator box and running along the floor to the rear seat. It's not hard, but time consuming. You must seal the leaks, let it dry and then retest before reinstalling the carpets and seats.

The guy I bought it off of said he had just cleaned the evaporator
(thats air-conditioning system-right?)
My hanes maual doesn.t seem to have any info on getting at it
I hear theres alot to take off to get to it
Do I need to take out the blower motor and dash components??
move the accumulator? some Underhood fuse panel?
Does anyone know of a good maual or web site that displays this info
A schematic or "3d" diag would be great
I'm not sure where to start but I will definetly make sure thats where the water is coming from before ripping into the evaporator job

You have to find the leak first. The carpets and seats have to be removed to see where it's coming in. It's not hard - just some bolts and wire connectors. Take you an hour and then you can see what you are dealing with.