Rog - take the top caps off and check to see if the stanchions slide down into the lowers without any problem.  If you've twisted them per the above, you'll find it there.  Also, losen all the crown bolts and take the axle out to free up any residual stress that may have built up in the fork assembly.

Other than that, they're fecked and need to be looked out!

To be honest with you I cant remember crashing hard on them before they became stiff, or anything else happening to them for that matter, just went out riding one day and realised they were real stiff.

Pretty sure I didnt damage any internal components when servicing them, I've checked everything and there doesnt seem to be any damage/score marks anywhere. I also made sure that all the old oil was out of the forks before I re-assembled them the last time. Ive also experimented a bit with the oil level, so Im pretty sure its not that.

One thing I have noticed though is that when I decrease the amount of rebound damping (make them more springy) then the overall sensitivity does seem to increase and they do seem to be easier to compress. This, coupled with the fact that there is definately something rubbing within the leg (due to the dirty oil), is what makes me think that there is something wrong internally on the rebound cartridge.