Check the rear engine/gearbox mount just in case (looking from underneath at the passenger side get someone to rock the engine backwards and forwards). Wear here can cause major problems with the gear linkages.
Also double check lubrication of the gear leaver/linkages. At this age of car the grease could have dried up etc.. The ball pivot below the gaiter can substantially stiffen up.
If it was the clutch it would frequently crunch going into reverse as I think there is no reverse syncro on this gearbox. As previoulsy mentioned try engagin gear with the engine turned off. I also think the clutch is hydraulic - double check the brake master cylinder lever to ensure you are not loosing hydraulic fluid (clutch - or brakes!)
Edited by Big John on 20/01/2012 at 17:14
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