Bad luck with the MOT fail, though it doesn't sound like much is wrong
Once you get it back, check the axle breather on the rear (and front) axle to make sure it's not blocked.
If it's blocked, that could be why oil has pushed past the hub seal (though of course, it could just be a worn seal

)
Very easy to do and a shame to pay garage prices so you might as well do it yourself.
Unscrew and shake it - it should rattle. Then wipe the threaded end off and try to blow through it - should be easy. If not, it's blocked.
They aren't expensive, but many folk replace the breathers with an extended kit to stop it happening in the future.
It's also recommended to fit extended breathers to overdrives and transfer boxes - stops oil being blown out of the breather hole etc.
See
SHAMELESS PLUG HERE for the kit I sell - contact me directly if you are interested in buying a kit at a discount for S2C and LRCC members
Cheers,
Robin.