Thanks for the heads up and the warning! I do have some information how to assemble and them how to remove the air. So I will see how I will get on.

So I started taking them apart. Firstly I removed the front shock from the lower 'leg', where it immediately became obvious it needed new bump stops.



To open up the shock the upper dust cup needs to removed using a flange spanner.



To get to the internals the upper cup with the seal has to be removed. It is held in by a circlip from the top. Firstly the gas pressure needs to be taken off so the upper cup can be pressed down a bit and the circlip can be removed.



When the circlip is removed the damper rod can be removed from the shock.



After that the oil can be drained from the shock housing. The oil in the rear dampers wasn't that bad, probably because the rear dampers have less weight to dampen and make a bigger stroke than the front ones.

This oil came from the rear dampers.



On the fronts the oil was a lot darker, so it probably had a much harder life.



And on one front damper the gas leaked to the oil. Opening the damper was like opening a bottle of coca cola after shaking it for a while.