My preference is the gear readuction starter from Expedition Imports. https://expedition-imports.com/starter-24v-gear-reduction-pinzgauer-pzgrst/ I've had 5 Pinz 710M's and used this starter in 3 of them. Much lighter in weight and much easier to install. They also spin the engine faster for quicker...
I'm not near my Pinz right now but as I recall you push the center pin (orange arrow) in with a pointed object and while holding it in, you slide the "bar" to the left (blue arrow). The ignition key is supposed to have a suitable point on it but many have worn off.
Are you referring to the large chromed ball, item #18 or #19 on the attached diagram? If so, I've found that carefully loosening and removing item #29, the seal retaining ring allows you to give it a good cleaning of accumulated grit, grime and grease. Then carefully re-assemble and tighten the reta...
It's not a bad idea to flush out the 3 hydraulic lines every couple of years. The fluid may collect moisture and become thicker and jelly-like which will make engagement/disengagement sluggish.