i've got the common problem with my 04 wr450f with 5th gear disappearing. had the gearbox apart and the dogs on 5th gear are so worn that they just slip out of the gear next to it. anyway, i was looking on a popular auction site and saw the internals from a wr400 and they look identical. so i've bid on them and got them for £16.50! and that's everything all gears, shafts, selector forks, etc... i've heard that people with yz 450's put the wr400 internals in to use on the road but i don't know if this is true. if anyone has any info or tips will be a great help.