any advise how to re-build that endo of the actuator?
I always strip actuators on the bench, not on the car, with the system de-pressurised.
Before taking the end casing off, undo the bleed screw and release the pressure. Even on the bench, they do hold pressure!
There are 2 small o-rings that seal the oil path to the rear plunger, which WILL be under pressure if the sytem is not depressureised.
Sorry, I forgot to mention this earlier
If you remove the end casing, torqx 20 screws, you'll access the steel shaft connector.
Theres a dowel in the front of the connector, which locates in the top sensor.
The large web at the back locates in the cut out on the rear plunger, and the rear sensor is spring loaded onto the web.
I don't have any pic's yet, but take care assembling it. For a trial, fit the web to the back plate plunger and get a grip of how the rear sensor works with it, before you screw it all back together.