I recently picked up a Toro Model# 20379 it has an oil leak at the rear of the motor on top of the deck. I noticed it after the second use and I haven't used it since.
Your best bet is to remove the engine shroud and see if you can locate the source. If unable to do so give it a very good washing, check the oil level, and run the unit watching for an indication of a leak. Watch carefully around the oil fill tube.