As title just put fresh oil in, and on the magnetic plug was bits of metal, the big bits are about 5mm is this a problem.

 

Yes, thats not normal wear. I would think about getting a 2nd hand diff as a spare incase it goes bang.

 

i would just replace it with good 2nd hand one as i couldnt be arsed to break down somewere or worse bust your gearbox when diff locks !!! , i have 1 here for import 4.111 ratio £40

 

HAWKEYE BEAST mines a uk my00

Just done the gear box 10 mins ago and i have a nice 1 inch bit of gear, not good as this is a recon say about a yr old, i no they dont last long if bootin all over or smokin starts but still not the best from just 240 horses. No point in fitting any more mods(VF34) till looked at or replaced