Soild Clutch Pedal

Afternoon all! My dear brother has managed to knacker the works 90 which is a 1986 ex mod with a 2.5 na. He tried to change gear but only got as far as neutral as the clutch pedal went solid and felt more like the brake pedal and so now will not disenaged the clutch.
Guessing the linkage was at fault we took the clutch pedal box cover off and found that one of the nuts on the master cylinder push rods was missing. We replaced this (blimey, they could have made a bit more room for my fat fingers) and found out that the other nut had slid on the push rod as the threads are slightly stripped.
It is obvious that is not the main problem and is the result of the clutch being solid elsewhere so that my brothers 20 odd stone stripped the thread off.
I then cracked off the union on top of the master cylinder and this freed off the pedal so it appears the master cylinder is fine and the problem is with the slave cylinder (new 3 year ago) or inside the clutch itself.

Can anybody suggest what the problem may be and how to fix it please? The Haynes book of lies is proving yet again to be particulary useless!
The 90 did do some wading at the weekend up to footwell depth, could it be water in the clutch making rust and not allowing the clutch plate to slide properly?

I'm off the take the slave cylinder off to see if that functions properly.

Cheers!

Could be that the release fork has collapsed/worn through on the pinion point, so the slave rod is fully out with nowhere else to travel. With a mirror and a light, you can look in the hole (with the slave removed) and see if the release fork looks intact and straight. If not its an engine out or gearbox out job. I did both within a month and would take the engine out any day, the 2.5N/A is a doddle to disconnect and remove, even with access to a hydraulic ramp I went for the engine out the second time round.

Thanks Discomania, sounds like good advice! I've took off the slave cylinder (keep thinking of Mr. Slave on Southpark-eurghh) and found that the release fork is pushed right to the back of its travel, so far that I can't even touch it. Something is obviously very wrong in there but can't find my dentist mirror to see but the engine is coming off anyway to get it sorted.
While the engine is off the gearbox, is it wise to carry out any other jobs as a routine, I was thinking of the oil seals on the back of the engine and front of the gearbox if that is possible?
The slave cylinder also appears to be coming to pieces, some fluid has leaked out and the piston would drop out if I allowed it. Shoudn't there be a circlip to hold that in? Could it have been pushed out as a result of clutch problems allowing too much travel? OR Has the circlip dropped out allowing the pushrod to bend the clutch fork?
All will be revealed with the engine out so I'm off the dirty my hands!
Cheers

Cheers discomania, you were spot on!

http://www.landyzone.co.uk/photopost/showphoto.php?photo=7799&cat=500&ppuser=6821

The release fork was worn through on the pivot. Fitted a new clutch while I was in there- not a lot left on the friction plate, release bearing knackered and the spigot bush was cracked. Engine came out quickly as the last person hadn't put all the nuts back on- engine mounts are a bit of a pain though. Hope I've put it together right!
Cheers for your help!
Tinribs