Selecting 4th Gear

[JPJ]

For a while selecting 4th from 5th has been a bit crunchy but now I cannot select 4th at all whilst on the move, either going up or going down both high and low box. I can select 4th when its stationary and move off without it jumping out. All other gears are fine.
I remember reading somewhere that a bent linkage could cause this problem.
Any ideas anyone?

[driftwood]

normally its either worn or damaged gear linkages or the synchroniser units that worn. i think from memory if its a selecter fork it jumps out of the gear but its sound like linkages/sync

[hobbit]

When was the last time you changed the gearbox oil?

That can sometimes ease these problems

[JPJ]

Thanks for the advice guys.
It looks like its 4th gear synchro according to various websites that I have been tracking down.
There's only one cure for this - and you guessed it - its expensive!  :(  or I just manage without 4th!