Jumping out of reverse

[rvfrc45]

Hi All,
I have friends that live quite away from me with a lovely low mileage Sprint, so
I can't just pop around the corner to have a look.
Just recently it has started to jump out of reverse.
At low revs pulling away you can just get away with it, slightly faster and out she comes.
I over the years have felt the sprint box pretty bullet proof so any thoughts would be welcome.
I'm sort of thinking selector Plunger/spring!!!
has anybody else had this.
Cheers Gw

[Jon Tilson]

I'd be looking at the axle tie bar bushes and prop centre bearing carrier before I looked at the box on this one...

Jonners