I am usually good in figuring where oil leaks come from. I've changed the chain tensioner o-ring which fixed the leak from the front passenger side of the engin. I have also changed one oil host to the oil cooler which is responsible for the leak in the driver side front part of the engin. I have also changed the oil pan gasket. Since then, I had gone under the car five times and still could not figure out the exact location of the leak which resulted in oil near the middle to the rear part of the engin. Oil appears to come from the driver side and extends all the way to the transmission. The upper engin block is clean, oil appears on the lower engin housing. Do I need the change the gasket? BMW dealer told me that I need to remove the engin to replace that gasket. I also suspect the oil return host which is connected to the lower engin case through a fitting. Is there any o-ring in the fitting itself? I hate o-rings in a ten year old car. Thanks.