GU Patrol Gearbox

Hi Everyone have a bit of a dilema here on what to do with the box in my 2000 4.2td patrol when i first bought the patrol the kind person ...haha ...i bought it off would always ask me to give him a call 20 mins b4 i got to his place to make sure he was home didnt think any thing of this , took the patrol for a spin liked it negotiated a price, bought the car , i'll just add that at the time i was living in Pt Lincoln and bought the car in Whyalla, anyway i drove the car home no probs , next morning i gets into car starts it up and ...WTF!!! is that noise anyway takes the car to mechanic and he says 5th gear is shot , common prob with that model , so i pays the money gets g/box recond mechanic shows me parts that are stuffed and tells me that it has been done once b4 and he thinks by nissan, well its been going great until about 2 mths ago i hear the same dreaded noise again, hoping its not same prob i try to ignore it ..lol....it gets noisier so today i decided to drain oil ..just as i figured its got heaps of metal filings and oil is a very metallicay color ...so if you were me would you buy an exchange box or consider getting this one fixed again, my way of thinking is maybe something not quite right in there ...bent shaft or something maybe???...what do you people reckon???....I was offered a box out of a 2001 GU td patrol ute today 70000ks havent worked out price yet do these boxes suffer the same probs ? and will it actually fit??.....cheers ......Dave