The easiest way to detect where an oil leak is coming from, is to start with a clean slate.
Buy some engine degreaser/muc off, and clean all of the oil off which has leaked.
Then, run the engine, whilst looking at the area, with a torch, so it's well illuminated and you should be able to see the oil seeping out.
The only seals which would cause oil on the alternator, are the cam cover & back of the head gasket.