window motor might have been changed in the past, and if they replaced the rivits with bolts they can eat tracks in the door panel and window would slide down or miss align, least its what mine did,, I fixed with lil bondo and fiberglass strips with resin. Might not be your case,, just a idea.
My '99 Firebird was leaking the same way. At the bottom of the U-shaped windshield pillar seal there is a drain hole and tube that sheds water down to the door jamb. I GENTLY reamed that drain with a coat hangar and water/black grit began dripping down the jamb. I followed up with a good blast of shop air in the upper drain hole and even more crap came out before the air started flowing freely. With the T top back in place I flooded the roof with a garden hose. NO MORE LEAK! But.... I noticed a NEW drip leak inside at the passenger side sail panel. I repeated the coat hangar/shop air treatment on the same drain hole on the rear seal, replaced the top, turned on the garden hose and... NO MORE LEAK there either.
No more than 45 minutes after I finished cleaning out the gasket drains the skies opened in a series of passing thunderstorms. I took the FB for a ride in the rain and no more T top leaks to be found. Seat and floorboard carpet nice and dry. ~FH