Anybody know exactly what was used on the top slider to have the slide engage the detents on the fresh air controls? There are detents for off, full fresh air (no fan help), fan speed 1, fan speed 2 and fan speed 3. I used a b.b. from a b.b. gun (I believe that’s .177) but there really isn’t anything to keep the b.b. from falling out. Not sure if originally there was a ball bearing in there (and if so what size) or some other part that attached to the slide. Pics of what I’m talking about below...

There are differences in the upper arms.
On my early top arm there is a leaf spring that retains the ball bearing that I added.
After cleaning the the disassembled unit and installing the ball bearing I has distinct detents that I had never
felt in any 914 (or 911) before.

I don't have a picture now, but there is a thin little piece of flat spring steel riveted at the open hole in your picture. Maybe cut a piece of feeler gauge to put pressure on the BB

I’m thinking about putting a small carriage bolt in there (something with a rounded head) and just a nut on the upper side. The b.b. held for a week or two but zinged out this morning while working the slide.

Ill hit the hardware store later today and see what I can come up with.