GQ Gearbox rebuild

Depends on the history of the car... if its been used for towing lots of things, then yes you could expect it.

Have you had it since new?

Havent heard of too many on the patrol list in the 2.8, so little shy on knowledge of them.

You could post there and ask.

Chel, unfortunately you have picked the Patrol with the worst gearbox. The "weak link" if you would. Certainly they are not suitable for heavy towing. The box is marginal at best. Unfortunately, when fitted behind the diesel engine and also asked to shift along some 2.5 tonnes of 4x4 and gear, it is at best, stressed. The seemed just OK fitted in 3 litre petrol models, but the diesel vibrations seem to further lessen their suitability of service. Some suggestions would be to use a top-quality lubricant such as Penrite with the adition of a friction modifier like Morey's, to cushion the bearing surfaces. Never fit oversize tyres (larger than 31/10.5x15) and perhaps consider an undersize tyre to lessen the gearing and load placed on the box. Of course, this may compromise other requirements like highway revs, ground clearance etc.

The 4.2 litre GQ gearboxes and other mechanicals are absolutely bullet proof. I have never heard of anybody (who hasn't totally abused it) ever having a problem....
I have a cousin who's on his third Patrol 4.2 who trades 'em in at 400,000 k's and he has never put a spanner to them apart from normal oil & filter changes etc (they have ALL been turbo'd after purchase)
Sorry- I know that doesn't help you....
After your rebuild I would speak to Mobil, BP and anyone else, and buy the absolute best synthetic lube available- Even if it cost a hundred's of dollars for the best oil (it won't be that dear) I'd buy it! Perhaps even a higher viscosity than recommended (might make the synchro rings struggle when the box is cold- but you could always do the old "double de clutch"...)
Good luck!

Would a G'box from a 4.2 fit ??

That would be your best bet!