the most common are windshield seals and hvac gaskets but literally every hole in the sheetmetal has leaked for some poor soul at some point in time. door seals, door windows, rear windows, fusebox seal, etc. Everything should be tested. I once had a leak at the top left corner of my windshield in the 86 that dribbled down inside the a-pillar and dumped out onto the floor at the kickpanel. if it wasn't for the powder trick I'd have never found that one. I had another leak in my 88 that originated from the seal at the back of the hood and dribbled down in the engine bay 'til it found a non-factory wire that poked through a gasket in the firewall that wasn't perfectly sealed up.
all should be suspect, all should be tested.