GT Greabox Oil

[clarkster]

I only changed my oil last year. Now ive got this noise in drive that i cant trace I thought id check the oil so I drained it off and it doesnt look great considering its only done say 5000 miles if that.

the best way to describe the appearance is when you open a new can of paint and after giving it a bit of stir you get that swirling look where the paint isnt properly mixed - mines looks like that between the normal colour youd expect of the oil and a dark greyish bitty looking oil. i stuck my finger in the drain hole but didnt pick out any debris. the plug had a decent amount of debris collected on it but i cant say if that was not there from the last change as I dont recall cleaning the plug off until today. grey tiny iron filing appearance.

the garage couldnt find anything wrong with CVs shafts brakes or bearings in the time frame they but they couldnt road test either. Does this sound like something in the gearbox or diff has worn like a final drive?
car is nosier than youd expect in all the gears and is worse at between 2500-3000rpm.

or does the oil get dirty very quickly anyway ? wondering for the price of 2 litres of oil if its worth renewing it again but the schedule suggests it only needs doing every 80,000miles

looked at the oil i used at the last change and its an 80w-90 grade of Castrol manual fluid but having checked the Haynes and the Porters i might have been using the wrong grade. porters says tutela 75w and haynes says SAE80w. i'll have to google what the additional 90 means
she's fighting me at the moment, is the GT.

[Mawbster]

autodatas listing 75-90 sae so i dont think youll be too far away to be honest.