I vote for the hole in the turbo plumbing causing your symptoms. They can be difficult to find sometimes. I use a plug the size of the turbo hose with a Schrader valve installed. Simply disconnect the hose at the turbo and insert the plug. Clamp the plug into place. Reduce the air pressure on your compressor to about 15 lbs. Apply pressure to system and listen for leak. Quick and efficient.

You will find that the cap on the master cylinder is the right size to fit inside the turbo hose. If you make a plug out of a master cylinder cap not only will you be able to locate holes in your turbo hoses but you can also use a bicycle pump to pressure bleed your brakes using the cap with Schrader.

Randy