Rear crank seal. If that leaks, engine oil can drip out of the bell housing gaps, but that's quite a rare problem on the EA113 to be honest.
Yeah I remember that nasty sh*t from school. Smelled of piss (ammonia) or fishy as you say! If it doesn't smell fishy, probably not DSG fluid then. OK so you have cod n chips to sniff out, or peanuts if it's the transmission side of the box. Pretty sure DSG uses a separate oil for the mechatronics and the gears? I don't know much about DSG I'm afraid. If it doesn't smell of either, it's likely engine oil.