I have a 93 LSS, and I've been chasing a driver's side leak(s) in it for a
few months. Here's what I've found:

First leak was coming through the door hinges on the "B" pillar. They had
rusted under the paint at the point of contact, creating a small path into
the car. A thorough wire brushing, and then a bead of clear silicone seems
to have solved it. Did the same to ALL door hinges on the car. BTW, a
friend's new Chevy truck has a bead of silcone in the same location! I guess
this is a known issue.

Current leak is coming into the drivers side floor, running down the inside
of the firewall. I believe there is a dried out gasket/seal in the cowl
area. This is the area you can expose by removing the w/w arms and then
removing the plastic protective piece that sits between the bottom of the
windshield and the fire wall. My current plan (when it stops raining) is to
apply some sort of mastic to the entire area. All it does is channel the
water across the car so it can drain inside the left fender. I have already
caulked between this trough and the rectangular piece of "duct work" that
feeds air down to the fan - the leak persists.

doug