i`m running a stock '95 lude, 5spd manual box, and UKDM (i`m a brit ya see)

it's grown a problem with the box, 1st thru 5th gear is fine. reverse gear would not engage. (this was last tuesday). i looked at it at work, and got it working that night - removed the rearmost cable from g/box, and used a lever to engage gears, reconnected cable and was 95% good - slight roughness coming out of reverse gear (all other gears are fine). it was alright wednesday, but this morning (thursday) i arrived at work, reversed up, tried to stick it in neutral but wouldnt come out. gave stick a wiggle and a few taps with hand, and it gave. it's now back to the way it was wednesday - 95% good, with the slight roughness coming out of reverse.

i admit that i`ve crunched the gears a couple of times (not had clutch fully depressed), but not used excessive force.

could i of streched gear cables, or is it a more serious gearbox problem? new cables are £240 in UK from dealer so it's not really a trial & error job.
any info appreciated.