Gear Problems! help.

I have a 300tdi defender and as of today, it feels like something is 'stuck' when changing from 4th to 5th.
It also feels the same when in neutral and the gear stick is moved from side to side.
It finds 4th perfect when changing up from 3rd, however doesn't slip straight into 4th when changing down from 5th anymore, but it does find it.
It finds 1-3 and reverse fine.
Any ideas!!?
Thanks!

I had same problem on my 300tdi when I bought it. Only mine wouldn't change down into 4th at all.
I'm afraid that I had to have box rebuilt.
Yours may be different - I'm no expert.
James Martin is the man to ask he sorted mine for me - He know his gearboxes - He reconditions them for a living. Where are you James ????