After realising that moving the PCB down a bit would not have the new arm arcing in a totally concentric way to the original tracks, I decided to try swapping in the two contact arm from the Porsche unit. The idea being the two contact points would be fully concentric and on new track material, untouched by the original three contact point arm.
Electrically I tried measuring the resistance of the carbon track and while there seemed to be some level of electrical resistance, I couldn't measure it with any consistency or confidence of accuracy.
As the Porsche arm spindle and top connector was different to my original one, I swapped in both the Porsche arm and Porsche contacts to it and the external connector. This was quite a painless process and aligned the arm to where the original had been. Turning it manually it looked like the two contacts were indeed on fresh track so put it back in the car for a test drive.
Wow. The flat spots in performance, especially at low airflow so in the area of the most worn parts of the track, were noticeably erased. It could be argued this was just wishful thinking but for me the proof in the pudding was the curved exit of one of my local roundabouts, which I normally take full bore in second gear with front wheels just beginning to spin as it goes above 4,000rpm. Today, with the rebuilt AFM, I actually had to lift the throttle to stay on the road - front end powering wide as both tyres were being over powered. So, wow. No imagination. The fresh track now in contact really has revived the AFM.
As for the Porsche unit, the same can be done there - with the original Alfa 3 contact arm and connectors being fitted there. Am very happy and wish I had done this years ago.