Nissan Repair: Nissan Navara gearbox problem., nissan navara, better mileage

Question
I have a 2002 Nissan Navara D22, and it has done 48k miles. It is serviced reguarly. The last time being no more that 6 weeks ago. For the last couple of weeks i have noticed that when i try to select 5th gear, it sometimes crunches and refuses to go into gear. This only happened occassionaly, but is now getting very frequent. I only have this problem with 5th gear. If i select 5th gear and hold the gear knob in position, when i let off the clutch i can sometimes feel the gear knob being thrown out. Do you have any ideas as to the cause?  

Answer
Paul,

Fifth gear and the baulking ring needs to be replaced.  Fifth is an overdrive and it receives much wear, expecially when it is not shifted down to fourth when accelerating.  Fifth is only for driving a steady speed to get better mileage.  Also, Japanese metal is soft and made of recycled material.  So, they surface harden it when it is manufactured.  Think of it like an egg; hard on the outside and soft on the inside.  If the hardness wears away and it happens to all transmissions if you drive them enough.  So, what has happened is the hardness is gone and the syncronizer and gear have blunted teeth, where they mesh, and that is what is causing the grinding.  Also, the softness has caused the fit to become loose and that is why it pops out of gear.  I would replace the components described in the first sentence.  Parts should go for something like $500 bucks and labor about $1000.