It's fixed!
Thanks to all of you helping to diagnose this fault. As it turns out, we were spot on. Indeed, the microswitch inside the pitch servo (KS179) had failed. I went to Avionik Straubing (https://www.avionik.de), who did an EXCELLENT job. They took apart the KS179 (see attached) photo, fixed the micro switch, overhauled the motor (so I get another couple of years out of it), and lubricated the mechanical part. Due to the clear diagnosis, they were able to focus on the work that was actually needed. As a consequence, the repair was still rather affordable (€1100). I flew PH-FAR back from Straubing to Rotterdam and tested the AP extensively. PERFECT!
Thanks again to everyone involved. This case is another demonstration of the value of mooneyspace. Signing off on this topic - Mooney Acolyte