There are many, many threads to search on this topic.
Water infiltration could be from more than one source. Perhaps the Windshield seals and the sunroof drains, for example.

Here is a list of candidates to inspect in order of likelyhood:
1) Open window (Close the window)
2) Rear windshield seal (Remove and Replace (R & R) OEM seal)
3) Front windshield seal (R & R)
4) Sunroof drains (Use Heavy duty weed-eater string to chase the drains)
5) Bonnet(Hood) Hinge drain channels (ditto #4)
6) Firewall breach under Battery Tray (patch holes, paint)
7) Door weatherseal (R & R)
8) Antenna mount (R & R)
9) Hole in floorpan (eliminate H2O source, patch holes, paint)
10) Tail-light Seals?? (I suppose it is possible with repaired bodies. Frankly, I've never experienced a tail-light leak)

After the repair get the interior as dry as possible. Sponge, Wet-dry Vac and place moisture absorbers in trunk and cab. I suggest you remove the plastic trunk liners and dry out underneath to preclude or inhibit rust, mildew, and that Godawful moldy smell.

Motor on

__________________
Bama1


2008 SLK 280, Firemist Red - "Hurricane"
2001 F150 Lariat 4x4, Black on Black - "Badboy"
1982 240D 4 speed survivor -"Pearl" - Donated to Vietnam Veterans
1962 Oldsmobile Dynamic 88 -"Gertrude"

1954 model original owner - ~2.5M
Gray softtop/solid exterior/modified chassis