Check around the front of the motor behind the crank pulley, front crank seals are very common on subarus when they get older, even valve cover gaskets. Usually the oil drips on the exhaust and burns off, that is why you wouldnt see it on the ground.
as far as the axle its pretty easy.
Jack up the car.
remove the 30mm (i htink its 30) hub nut.
remove the roll pin that holds the axle to the trans stub shaft
remove the two strut to knuckle bolts, mark the position of the top bolt at 12'clock (camber adjustment) in order to put it back in the same position. Keep track of the washer on the nut for that bolt it has to be reinstalled on the top bolt.
Pry the axle off the tranny stub shaft.
Hammer the axle out of the hub.
reverse the procedure for installation, make sure you line up the hole in the new axle with the hole in the stub shaft before you push it on, there is a chamfer on the axle roll pin hole that has to lined up with the chamfer on the stub shaft roll pin hole, install a NEW roll pin.
reassmble the rest putting the top camber bolt back in the same position.
get an alignment.
hope that helps. You may or may not have to remove the calipe and tie rod from the knuckle for more clearance to get the axle out.