Chute55uk, Wrong forks.
These are air/oil
What exactly do you need to do ?
LEAVE the oil in, LEAVE the top caps on. Best if the air valves work reasonable.
Take the brace and crown off.
Take the dust wiper off. (small screwdriver on find the bit that looks like it should go in there. twist and lever it out work your way around. top ring of paint usually comes off.
Drop some oil/spray into the bit under it and clean up what you can.
Take the circlip out, careful not to scratch the stanchion, more so if it '94 Gold Alu ones.
More oil on the oil seal there, penetrating around the outside edge if you really need to.
<might be good to leave on a hot radiator laid down for a bit also>
Now wrap the seal area in a teacloth etc..
Find someway to hold the lower legs and pump air into the top but also keeping the stanchion under control.
Pump air in, as much as you need, shouldn't need to go too far over 100PSI , if you do I would stop and try and get some oil/penetrating, heat expansion expansion going around the oil seal and try again.
< think what might happen when 100PSI suddenly blows the oil seal/stanchion away from the lower leg by oil pressure >
You might be lucky and it just pops apart easily at the lower pressure, or even pull apart with no air, but the negative spring usually makes that difficult in MAG21's. MAG20's don't have the spring to worry about.