Big smile :>)

Good balloon test! There will not be enough pressure in the crankcase to inflate a balloon unless you had a leaking headgasket or bad rings. What you noticed was the turbo cranking a little and introducing positive pressure in the intake and removing vacuum at the PTC, instantly corrected by the system.

The oil cap is directly over a cam and the cam spits oil onto the cap. A hard seal or cracked seal will allow a lot of oil to be spilled past the cap, which can seep anywhere. I think you solved your problem.

The turbo oil return line has nothing to do with the PCV. When it leaks, it leaks and needs to be repaired.

The most common problem with the PCV are the aging vacuum lines which can crack or get plugged with oil. Turbos are vulnerable to the PCT nipple getting plugged and no longer functioning, similar to the PCV in NA engines.

Klaus
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Always willing to listen, just not able to take direction.