VR gearbox playing up?

[EnviusVScom]

Gday guys Ive got a 94' vr ute with a 5 speed, its 5th gear is noisy, its a kind of light grinding noise. And also it wont shift down into 3rd from 5th, 4th or even N, but it will shift up into 3rd fine. Can anyone tell me what that might be? and is it worth getting it fixed or just replacing the box.

 

[Dr.304]

Change the gearbox oil straight away. Throw some of that nulon teflon stuff for gearboxes.
If it is still playing up after that, change it or get it checked by a mechanic.

Check owners manual for number of litres required. I think around 6L?

 

[EnviusVScom]

Do I have to get it done or can I do it myself?