My 300e had a leak, which I though, it was on the rear cover. After close inspection, it turned out to be leaking from a bad O ring from the sensor attached to the side of the differential. The fluid would travel towards the rear due to forward motion of the vehicle, so it would seem to be leaking from the rear cover. The O ring cost less than $2. Take a second look, you won't loose anything.
Good luck!
