What condition and age are the tires? Nice interior to me means perfect seats, crack free dash, and wood trim.
Does the sunroof work?
Water in the cabin is indeed a huge potential problem. Pull up the carpets, find where all the water is. All of it.
Dry trunk is good. Open all the doors and inspect the seals. The doors should have seals that fill the gap when closed.
I'm at about $1500 bring an old ovp with you to test the car out. Try the ovp. Find the leak. Look over the sunroof very well. Look around the BATTEY AND THE BRAKE BOOSTER for signs of rust. Water getting in here is a serious pain in the butt to fix.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!