Nice Joachim
I've been playing with this servo in LTSpice as well.
Here's what I came up with...
I added a 1K resistor across Q5. I didn't have R17, but I like it and it seems to model better. D2 is probably not needed but wanted to protect Q5, just in case.
Have you tried it without the 2.2pF cap across the 2 Meg resistors. I'd prefer not to use this.
I'm enjoying the show