Hi dan, EXACTLY the same thing happened on my JTD. The mechanic thought it was something to do with one of the little selector ball bearings in the gearbox. Anyway, i seemed to notice it more when the car was on long journeys!
Anyway i bought some STP gearbox additive and some Gearobox oil (the best type, think it was castrol - halfrauds recommended it) and changed the oil. Really easy job to change the oil but you may need the big allen keys to do it (sorry dont kow the size of them! someone on here will tho)
When i changed the oil there was some metal shavings on the drain plug which i cleaned of beofre i replaced it. Since changing the oil, 4th gear still feels a little stiffer than the others to go into but it is far better than it was and im hoping it will just ease up the more i use it. My mechanic says that gearboxes are the sort of thing you just hae to run into the ground before replacing them!
PS maybe try adding to lots of the gearbox additive?
Hope this helps!
Stu
(currently in argentina!)
