5 In a row

I've got a 4 year old car with 28k miles on it. In the last few months its had a squeak coming from the gearchange when going from 4th to 5th, unless the change is carried out at old man speed. The garage have had a look and diagnosed a dried out balljoint in the top of the gearbox and said that the problem will spread to other gears. They've greased it but that's made no difference. The change itself is as good as ever. The cost to do this is going to be around £400 and, obviously, the car is out of warranty. Anyone else had this problem?