Have someone that can give a second opinion? All too often I have heard this diagnosis and it winds up being something above that area. It just happens to be the lowest point where the oil drops off the engine, so they assume it is the main seal. Plus it is a nice payday for the dealer.
Never worked on that particular motor, but in general, VW/Audi engines rarely leak at the rear main. On most of the VW/Audi engines there are a few slots/holes between the engine and transmission that you can shine a light through and tell if indeed there is oil coming from the seal or above it. Good luck.