It could certainly leak from the bottom crankshaft seal: where the crankshaft comes out through the crankcase cover, which you call the oil pan. That oil seal sometimes is damaged by something being picked up and getting wound around the crankshaft, above the pulley. However if it were leaking from the crankshaft seal you would see oil running over the pulley, and there would be oil on the drive belts.
It is relatively unlikely it would leak oil from around the outside of the crankcase cover: it would have to have been badly reinstalled during a repair operation.
Can you post pictures of the engine right where the oil seems to be coming from?
