A second gear crunch is something infamous on mk2's due to the fact people do a rushed change ("racing start") from 1st to 2nd and fudge it up, the more it happens the more damage occurs. The start of the syncro wearing would be a notchy gear change, possible crunch when the gearbox oil isn't up to temp but when it is quite worn you would hear a bad screech/crunch. 3rd gears have been known to have this same problem too.
Check the plastic linkages for cracks, the relay shaft ball etc for correct location (maybe post a pic) then after you could try changing the gearbox oil. This will not cure the problem, but just mask it unfortunatley.
New box is pretty expensive so hope you find its something else.
