Last 2 4wd NV4500s I bought that "needed 5th gear fixed" had major issues, with the last one having 3rd gear (not 5th) physically broken, as well as the accompanying gear on the cluster gear was destroyed.
The one prior to it had a key/ball assembly from the 5th gear synchro assembly drop into the gears, THAT one had a 5th gear issue, but not what you'd think.
My point is, make SURE that what you say is wrong is actually wrong, else you'll have a really, really, really pissed off buyer for that much money.
Mark.