The rubber busings in your gearbox just make it smoother and easyer shiftin. They wont be causing the shifter to jump out of gear it is the sincro mech in the 5th gear selector fork, You can just open up the housing and do it yourself for next to nuffin but its not worth pulling apart unless you know what ur doin, if you are goin to pull the box apart you might as well do all of the sincros at once im not sure what the cost of sincros are over where you come from but u can be sure if u do the one no long after its back in another will go. patt