how do i find out where oil is leaking from the back of my car

Hello, Check your turbocharger and intercooler tubes. The turbo is probably losing the central housing oil seal, so oil will pour into the high pressure tubes. If your turbo/intercooler piping (all on the cold side) are dry inside, you may have a leak at one of the oil supply lines for the turbo. Porsche/VW/Audi are pretty well known for turbo replacements as they age. Your owners manual should specify it, but remember to check your oil every time you fill with fuel. Even the economy VW models with turbochargers recommend it. Doing so will help you gauge the turbos point on the spectrum of oil consumption. If you are losing more than a liter every 1000 miles, pull the exhaust downpipe off the turbo and see how much play you have on the impeller. Very little is ok when there is no oil pressure.