Don't be to hastey with changing the fork, it could be any of these parts:
slave cylinder
master cylinder
damper
fork
If you take the front prop off and gently slide the slave cylinder off of the push rod thats connected to the fork making sure you don't pull the push rod out because thats alot of hassel to fix back in.
Once thats out you can just about get your head up there to see in the hole where the slave cylinder was and you can see where the fork pivots and more importantly if its shot.
I thought the fork had gone on mine once, took engine out instead of gearbox because its easier, replaced fork, clutch plates, spiggott ring and bearing, put it all back together only to find out it was the master cylinder. But hey, it was good experience.
Hope this helps, Mike.