Those turbos seem to last forever. I had one rebuilt because the turbo was whining a bit. The rebuild was relatively painless but did not stop the noise. Of the things you have done I would suspect valve seals first.

As far as I can tell, the smoke at idle is gone. There seems to be a tiny bit of blue smoke (as viewed from rear-view mirror) all the time, but I suspect that is from it having 306,000+ miles on the engine.

well, yeah there is always that.;)

My smoke might be turbo seals. If I do a hard high rpm run for a mile and stop at a light I get a little smoke. It clears up after a few seconds while I’m waiting. I’ll start reading up on rebuilding the turbo.

I had the exact same issue. I too had to take the seat backs to my local upholstery shop and have the covers modified to fit the seat backs. The shop went against my wishes and backed all of the leather on the side panels with some kind of thick material, and that made it very difficult to install all the hardware because of the extra thickness. DON'T let them do this to yours!!!
In the end I made the covers work, but was not happy with the way the shop did them. I also probably paid too much. I hope I have learned something from the experience.