Start by treating your weather stripping with the correct silicon lubricant.
Like "HPG", I've experienced a leak around the A-pillar before and decided to add a little extra between the roof and the windshield. I put a little extra silicon sealant (aquarium stuff) on the weather stripping between this two areas, placed some wax paper between them and bolted the roof back on. After the sealant cured, I removed the roof and the wax paper and pressed on. This provided the extra sealing needed to keep the rain from dripping on the floor. Over the years, I've taken to treating the weather stripping with a proper silicon lubricant treatment on a regular basis and have had any return of the problem. I drive my old 92 daily, rain or shine.