I had this problem not to long ago. Thought it was temperature related as it got worse after a long drive or after sitting in traffic for a while. Turned out the 3 of the 4 spot welds had broken away from the clutch bracket on the bulk head, think it got worse after sitting in traffic for a while because the bracket flexed even more and hence got less clutch travel. Could be worth a look.
Dont think the clutch fluid actually gets that hot, worth changing though. Think the best way is just to connect a hose onto the bleed nipple and bleed all the old fluid out into a bottle or somthing, top the reservoir up as your doing it untill new fluid starts coming out the bleed nipple.