Here is a picture from the parts catalogue:
Remove the wheel and the front mudguard.
Unscrew the cap screw 17 and remove the washers 18 and 19.
Release the clamps 42 from the boot 40 and push the boot down the fork.
Remove the grease fitting 6.
Unscrew the nut 34 which screws into the bottom of the outer tube 5. I used pliers for this, not the best solution but it got the job done.
Leave the screws 8 tightened.
Pull downward on the inner tube 24 or 27; the assembly of the inner tube, Pertinax bushings, and springs should slide out of the outer tube 5.
It's possible that the bushing 35 could stick in the tube 5, but tapping lightly with the inner tube should help it come out.
You can then remove the springs from the inner tube 24 or 27, possibly by removing the pin 29, but I simply unscrewed the spring 30 from the fitting 28.
Now you can remove the screws 8 after which the outer tubes 5 can be removed downward from the steering head.
The sleeves 2 in my case stayed in the steering head. Rubber rings 39 fit at the top of the headlight brackets 3 and 4, rather than at the bottom as shown in the picture.
For me, reassembly was the reverse of disassembly with these particular points:
I had to make new spacing washers 36 and 37 as they were missing from my bike. Tolerances of the inside diameter of 37 and the outside diameter of 36 are small as both washers fit against a shoulder 0,5 mm wide.
Install the spring assemblies in the inner tubes. Then place in the tubes, in this order: 40, 34, 35, 36, 37, 38, 39. Tighten 39 on the upper Pertinax bushing. Then slide the entire assembly into the outer tubes 5 (parts thoroughly greased). Tighten the nut 34.
Insert the assembly into the steering head, pressing upward until the outer tube is seated in the upper bracket 15. Compress the springs by pushing upward on the inner tube 24 or 27 until the screw 17 can be started. Turn the inner tubes 24 or 27 in the direction of tightening screw 17 until you feel the dogs at the top of the spacers 32 enter the slots for them in the upper bracket 15. Turn the outer tubes 5 so that the grease fitting 6 is oriented appropriately (I faced mine rearwards) then then tighten screws 17 and 8. Then do final tightening of the nuts 34.
I think that's all there is to it. If it's not clear, just let me know.