Replacing hall pickup in Bosch distrubtor

[Krampus]

The header on my distributor cracked, although the wires are still connected and it works fine. I pulled a replacement at the junkyard, but now I'm trying to figure out how to disassemble my distributor to put it in. The manual shows that there is supposed to be a circlip and aligning pin on the top, holding down the trigger wheel. At the junkyard, I destroyed two trigger wheels removing them (first hall sensor assembly looked fried so I snagged another) using a method as close to the Bentley manual as I could manage. I obviously don't want to repeat that a third time on a distributor that actually matters.

Does anyone know what the trick to getting the trigger wheel off these '88 version of the Bosch distributor is? Again, there appears to be no circlip or alignment pin on top of the trigger wheel. There is a ring at the base of the shaft, but it doesn't seem to be holding the trigger wheel down and doesn't look to be a circlip, unless the gap on the ends is thin enough that I couldn't see it or feel it with my probe.

[Krampus]

Answering my own post since a dealer ordering a new housing for the engine speed sensor on the distributor included a diagram from VIDA that shows the solution. It doesn't look like there's a circlip on the '88 distributor holding down the trigger wheel; It's attached to the timing shaft. To remove it, you have to pull the whole distributor out and knock a pin below the drive sprocket to release it. After removing the trigger wheel/timing shaft, the hall pickup is just screwed down.