Hey BigRed,
Mine isn't a C4 like yours, but I dealt with my share of leaks for several years!
I saw great improvement when I replaced my weatherstriping on the doors, pillars and t-tops. I also had my windshield re-set twice. The second reset appeared to have fixed the leak I was getting from 'under the t-tops', I think it was actually coming in under the moulding/flashing(?)
I treat my weatherstrip regularly with die-electric gel, and someone mentioned to me that I should periodically loosen or remove the t-tops to allow the weatherstrip to 'un-crush' and make a better seal when re-attached.
I currently have a leak over my shoulder, too. This is due to poor window alignment that will be getting corrected soon as we can hook up with a friend with the know-how (who does this type of repair all the time).
Until that happens, I keep a towel over my shoulder, like I'm burping a baby. I also pull the seats forward and tilt them to the front, draping a towel to catch any drips that occur while 78 is parked. I have found that it is usually the driving wind's pressure that forces the leak, and if it is raining lightly, I have no problem. I don't like to drive in heavy rain, but that is only due to not wanting to hit a pond in the road and have it throw me into oncoming traffic or off the road.
I like the look of a wet 'vette! They look clean and sleek with the water all beaded up on them!
Silver