While you're under there getting showered with Castrol GTX, I would recommend you check the area inbetween the oil filter housing and the block. It is a common source for large oil leaks. There are two gaskets, one inbetween the housing and the block and one that is part of the two-piece housing. There are 6mm allen head bolts holding the housing to the block. They can be a little difficult to access but once resealed, this eliminates one major area. Next check your oil pan and the return pipe from the turbo to the sump.

__________________
Regards,
Aaron