GQ gearbox

I have an '89 4.2 diesel GQ, which now has a small hole in the passenger's side of the gearbox in-between the transfer case and the main housing of the gear box (I think it's the adapter between the gearbox and transfer case). Something has punched a hole from the inside of the box, dislodging a cylindrical piece of metal (with a square end). The dislodged internal part is partially filling the hole.

I can still select all gears including reverse in 2H, 4H and 4L. There does not appear to be any noises from within the gearbox indicating that something inside is broken ie. no bearing noise and gears aren't hard to select.

Prior to discovering the hole there was a tapping sound coming from near the gearbox. I assumed that it was a stick which I had discovered wedged between a body mount and the floor... Now I am not 100% sure whether the noise that i heard was the stick or the box.

As Patrols generally have few major problems with the gearboxes, I was wondering if any one else has had a similar thing happen, or would be able to shed some light on what may have happened?

I am unwilling to drive it anywhere at this stage since the entire contents (gear oil) have emptied onto my garage floor.