gearbox might be on its way out?

I've read parts of the gearbox problems, but not all of it and theres far to much to go through to find what I need, basically, my gearbox is fine, apart from high revs driving quick, it struggles to go in 4th, crunches and grinds, does this mean my gearbox is on its way out?
 
Definitely sounds like it.

Any crunching in high revs is a sure sign of a faulty box.

Mine was fine in slow revs really. But upshifting into 3rd always used to crunch.
 
Well you can always try Renault for help but it depends on age of car, milage, service history with Renault and your history with them.

I'd hazard a guess it would be a lot cheaper to buy a box from RSC and have it fitted.

Box is circa £400 iirc and labour is around 5 hrs.

I'd also fit a new clutch