can't you glue magnets to the white wheel at the end of the main worm gear axle and put a reed sensor on a bracket that is nearby?
There are a number of different configurations in the field.
In trying to come up with a universal kit, I couldn't assume any particular hardware.
Some users had a factory (?) mod with an 8-magnet wheel at the end of the main worm gear where you describe.
Some users had a little plastic white gear there, to turn the pot.
Combining any sort of magnet, 20 year old unknown plastic, and a glue to bond them, is a recipe for trouble.
Even how the end of that shaft was machined... seemed to be hard to document.
Some had a little hole in it, but even after asking a lot of questions and examining a lot pictures, I couldn't be sure everyone had the same hardware.
Locating the wheel between the other end of the worm gear and the motor right-angle gearbox as Linuxman had done, seemed the most universal location.
Phlatwound seemed to agree, and made a nice template for a 24-magnet wheel.
Even if you come up with a one-of-a-kind solution, the above is a proven concept.
I ordered up about 400 very tiny magnets and some ultra small reed switches.
...oh, be sure to use an EVEN number of magnets, and ALTERNATE their polarities around the wheel ! -
Was working on some prototype wheels, but winter came and my co-conspirators went off to hunt deer or something and I never got back to it. -
Oh, and one other variation in Birdviews, too.
The casting went from a rough sand-cast to a smooth die-cast piece over the years of production.
Not sure if that would matter or a universal reed switch bracket could be built.
Phlatwound has both types and has published some of the best pictures we have of the Birdview castings. - :up
Linuxman has a big fleet of the dishes.
Look for his pictures, documenting his success at making the first 24-magnet wheel!
That was the initial groundwork for all our ideas since.