So check this out. As I was pulling the wastegate off, I heard a klank and looked down to see the wastegate valve on the ground. Umm, that's not normal.
I took it apart and there are the 4 set screws that secure the diaphragm to the valve, just banging around loosely on top of the diaphragm. That explains the valve falling out and it also explains something else... when I had boost-leak tested the car earlier, I couldn't figure out why I was getting boost all the way through the wastegate. I figured the diaphragm had popped out or gotten damaged somehow, but luckily that wasn't the case. It was just blowing through the screw holes.
As for the screws backing out... I know that I put them on tight. I know I did. What I didn't do is clean them and re-apply threadlocker, and I'm guessing that was my issue. I cleaned it all up and applied some high temp threadlocker called Resbond, which I had left over from my Inconel turbo stud kit. Unlike other thread locking compounds, it holds up to high temps very well. I put the screws in good and tight with the Resbond, got it all back together, and she's back to normal now. I actually thought something was wrong on the first drive. I couldn't understand why it felt so slow. And then I realized the boost controller was just off.
Even low boost, 12 psi, feels so slow now.
I'm starting a new job this week, so updates are going to come more slowly. But I am determined to get the car on the Nismotronic SR ECU soon.