Hi. I have a Quattro and on the MOT they picked up an oil leak from rear of car, so i guess its the Quattro system

Anyone know how much i will be looking at to repair, depending on what it is?

It cant be a bad leak as its not left any parches on drive or work space?

My other worry is how long i have had the leak, I have booked it in for a service next week but use the car a lot!