There is an crankshaft oil seal, it MIGHT be changeable without a teardown but I can't guarantee that. It is shown as a standard size but it may have retaining tabs, I don't have one here or an engine apart to say for sure. A standard oil seal should be removable with a seal hook or home-made tool and the new one would drive right in, retaining ears engage notches in the crank split and hold her tight in place. You can not see the ears with the seal in place.
The alternator cover isn't really sealed, the wires come out at the bottom through a split grommet thing .
Oil shouldn't hurt the alternator, however it really shouldn't be leaking down the crankshaft. If it isn't a gross leak dripping (or poring) oil out I would live with it until maybe you need to tear down the motor.
Another possibility is the oil gallery plug below the crankshaft, it looks like an aluminum nipple on the left side. Pull and twist on the nipple with pliers and it will pop out, there's an O-ring seal that might be the problem. Some oil will come out (a cup or so) but I think (heh heh) it's above the full oil level in the engine sump. DO NOT start the motor with the alternator cover off as the cover retains the plug, oil pressure will pop it out and you'll have an unholy mess.
Getting the alternator rotor off requires a hardened threaded tool or bolt, the rear axle has the same size thread but using it tends to result in stripped threads both on the axle and in the rotor.
