Q8, some diffs. do have a breather, my Caterham uses a Ford Sierra diff, and that has a breather. It's a little rubber tube that goes over the top. I guess it lets air and gas from the oil out.
The bevel box shouldn't throw oil out of the breather, it's either been overfilled, or if it continues, there may be a part missing, although I haven't looked, it will possibly have a small plate covering the breather to stop oil being thrown directly out of the hole.
