Today been on along run of some 300 miles roundtrip. But had a strong smell/fumes of gear oil in the cab.

Although I know what seems that when serviced last they had not sealed the transfer box drain plug and the housing is wet from being blown back and the oil level has been topped up over the weekend.

Would this be a sign of Gearbox or Transfer box problems about to start, also any clues of where the fumes etc could enter the cab.

thanks

They spilled gear oil in the cab, which caused the gearbox to asplode, drenching a small mouse who, terrified, sheltered the dash, and is now running a tiny gear oil factory. This is what you're smelling. Feed it.