If the oil is seeping out from the very centre of the wheels (the hub / end of the half shaft) make sure that it has a rubber hub cap / bung over it like this:
FTC5414 Hub cap - rear axle from LA930456 which will stop any oil from leaking out.
They need to be dropped into a bowl of boiling water to soften up before fitting and then once they're on the only way to get them off is with a stanley knife, right through the middle.
If is from the drive flange (the bit with 6 bolts or so) you can just unbolt this, pull it off, clean up the surfaces and apply some gasket goo and then bolt it back on nice and tight.
Job done
-Pos