Clutch or Fluid boiling problem?

Hi Folks just found this forum and signed up.During late August,we took our caravan to Spain,Heading along the A23 towards Valencia,This Dual carriageway climbs to 900 mtrs elevation.Any way,the temperature was in the 30,s as we wound our way up some of the steep inclines,never allowing the engine to labour,and keeping the revs to about 3000 rpm When suddenly,as I attempted to change down,the clutch pedal went to the floor.We decided to soldier on to the next services where we lifted the bonnet,examined all around for any fluid loss,sniffed around for any smell of a burning clutch,and came up blank.The wife and I agreed that the best course of action would be to leave the car for an hour to cool down and then reappraise.After the time had passed,i jumped back in started the engine,and low and behold the clutch pedal had returned to normal.We completed our trip to spain and have not had a problem since. Has anyone out there any clues as to what caused this,and what steps could be taken to avoid it happening again? The car is a 2005 Freelander TD4 sport 5door manual.With 62000 miles and a full service history.

Had this happen once - just once !
I believe it was the slave cylinder (conveniently located inside the bell housing) that was naff
since then i have replaced the clutch and the offending slave cylinder

so far so good

the fluid would not boil as it only gets used when you change gear but i would get it sorted before it goes much futher probably like digby said slave cylinder and while they are at it have a new clutch it could be that as well climbing all those hills