Right, I was scared to do this myself because if you get it wrong then it can hurt, well that was my thinking back then.
I now know, thanks to YouTube, that it is realy easy to replace the oil if there is nothing wrong with the seals, and this how you do it okay.
First you remove the steering damper from the bike
Okay jokes aside.
Go buy youself some fork oil, I used Silkolene 7.5W racing oil. 1 Litre bottle.
Get yourself a 2L ice-cream tub (empty one
A. Remove the Allen head grub screw which sits opposite to the tension adjuster knob, also turn the adjuster to the fully "hard"position.
Now there is two ways to go about with the next move. I will show the one way only.
This is the easy way but the "you have to be more carefull at the end way".
B.Turn the damper upside down into a jar and move it up and down on the rod - you will see some very ugly oil come out and also a fag filter like black sponge - then a black metal tube about half the size of a fag will fall out, remember which way round this goes back in.
C.Once you have moved the casing up and down the rod till no more oil comes out, you place the entire damper in the ice-cream tub and submerge in oil that you already bought remember. Also turn the damper adjusting knob to the "Žasy" setting.
D. Have a Beer
E.Now this is important - keep the damper submerged at ALL times from here on in. So make sure you have all the bits you removed right there next to you and some clean rags.
F. Now slowly move the damper to and fro on the rod - I found keeping one of the ends on the rod makes for a good place to grip - and now winding the adjuster knob to the "soft" setting if you have not allready done this - keep doing this slowly until all the left-over oil had come out and had been replaced by the new oil. But more importanly, till no more air bubbles come out.
It is very important that you can not feel any air inside the damper, so keep doing it till you are sure you can neither feel or hear any air.
Your last movement is to be with the damper sucking oil IN, so make sure you become clear on this as you suck oil in and blow bubbles out.
G. Now, while still keeping the damper submerged, insert the metal tube with the smaller end first - push it all the way in using something like a scribe - till you can see the thread for the crub screw. Still submerged !
H Now submerge the sponge - squeeze some oil through it to fully empregnate it - and insert it into the damper.
I. STILL submerged.
Now fit the grub screw back it and tighten with a Allen wrench.
Okay now you can take the damper out, wipe it and test it.
Make sure you have NO air in the damper my moving it around and operating it again.
If you hear air bubbles, put the damper back in oil, remove grub screw and insides as before and repeat the steps from E.
Good luck, I did this with my damper and was pleasantly surprised by how big a difference it made, and also how dirty the oil was inside there.
Have another Beer on a job well done.