peugeot 406 gearbox

i have a 2.0lx estate 406 and cannot get it into reverse properly when i do
get it into gear it pops out within a few seconds all the other gears are
fine is this a linkage problem or is the box no good

 

The Haynes book says.Jumps out of Gear due to worn or Damaged gear
linkage.2.Worn synchroniser unit.3.Worn selector forks. so i think you
might have to remove the box and replace it with a rebuilt one unless
you are good to rebuild it your self.
what you do good luck. from Chris Addlestone Surrey

 

thanks mate car has been in garage and a new gearbox is needed