Offroad-Express

I seem to be experiencing a few problems with my 60 series 5 speed box. It's started jumping out of some gears, and hard to get in others! It used to jump out of 2nd occasionally, but now it's 3rd and 4th too, and alot more often. Time for a new one? (gearbox that is!). Is an exchange box the way to go?

my 5 speed used to do that, the bush that supports the gearlever had worn and half collapsed, I was told its a common problem when they fixed it