Yes, if all the other gear changes are OK then its third gear. Secondhand box from a breaker if your on a budget. You will probably have to change the clutch disk when you have the box out so factor that into the bill.
Double check the oil level in the gearbox if you want to cancel all the easy stuff out. But most likely the level will be fine.
You can change your driving style and see if that helps. The box could last forever if its not abused. Try jumping third, or a slower change might help. You could always try the link below.
Imagine two gear shafts that need to be coupled together.....if they are rotating at the same speed this should be quite easy, right? This is done by the synchromesh cones in the gearbox. Once the shafts are at the same speed, they are locked together by the synchromesh hub. So, if you have zee crunch, its the synchro cones that are tired. Chances are the gearbox will go on for ages, and it will start jumping out of gear before the crunch gets worse.
John
Thanks for your reply,did wonder whether it might be the synchromesh on the way out,kinda hoping it was something else!Another gearbox needs to be sourced!