I have shopped around some body shops in the area and found Elhot Metal Fab recommended by someone on a Porsche board (http://elhotmetalfab.com/). I decided to drop in one day, and instantly liked Elliot, the owner. He had a MGB, nice early 911, a Jag e-type on a rotisserie and a 356 convertible in his S. Lake Union shop, a one-man operation. He was amenable to taking my car on bit by bit, his hourly rate is very reasonable, and he had space in his schedule the following week. Best of all, he said I could do some disassembly in his shop. I took out the headliner, carpet, seats (except drivers), quarter windows at home. Discovered nice rust under the quarter window bases and inside the roof. In his shop, out came the windshield (a bit of rust under the seal), sunroof panel and guts, and the drip rail chrome (more rust).
I grew up in New Hampshire where cars rot from road salt from the bottom up. Here in the Northwest they rust (more slowly) top down from rain, and also from condensation inside the car. BMW put foam in the roof under the headliner which acted like a sponge to keep moisture against the inside of the roof panel, which had very little paint--bad combo. Leaky window gaskets let more moisture inside, and when it tries to escape, it gets stuck under the roof.
Elliot didn't like the look of the roof clip I had bought, which was only slightly less rusty then the one on my car, so he cut out rusty roof metal and quickly fabbed up new replacement steel. He POR15ed and epoxy primed the exposed roof frame. He had to get a subtle compound curve into the new steel, using cool old Boeing surplus metal bending machinery. Wish I had those welding skills.