Well, I'm sorry to report that a rusted windshield frame is the cause of the leak.
I pulled the rubber molding out from its channel at its left end (it was partially glued in because some of the white sealant used to seal the cap had oozed onto the molding track).
The steel was heavily rusted in a 4 inch area near the upper left corner. The rust extended under paint and sealant so I cut that out too where needed. I'll have to cut out a portion of the plastic tack for the molding because there's rust under that too.
Because the rusted area goes to the corner of the frame, I had to remove the large painted fiberglass side molding. The link helped locate the 3 nuts, two phillips screws and two allen head screws.
The condition of the rubber molding is good, so I'll not replace that.
The rest of the top of the windshield frame is completely covered by the white cap sealant or by the black windshield adhesive so I can't see any underlying rust there. I think I'll leave that alone because cutting it all out to search for rust underneath would be a lot of work and maybe unnecessary.
After cutting a portion of the weatherstrip track out and hopefully finding the endpoint of the rusting, I'll clean it, coat with POR 15, and then look for a very sticky, non-hardening sealant to go over the POR 15.
Does anyone know how the plastic weatherstrip track is attached to the windshield frame?
If a photo is helpful for others, I'll try to post one.
