Chat Gearbox making noise and crunching into 3rd gear

[Loopylou]

So had the clutch done today and my mate also noticed the gearbox seal needed replacing as oil had been leaking out. Problem is once it was all put back and he took it out for a spin he noticed a rumbeling in the gearbox, also for a while now it crunches into 3rd gear if the revs are over a certain point, if i let the revs drop before changing up it doesn't crunch.. Also every so often when your in 5th it seems to spot it out! Any advice be great