Yup, I'm pretty sure it is both an internal leak on the M/C and a leaky booster. It is intermittent but is most noticeable when first starting up. After you press the brakes a few times it works better, probably just means the seals start to half way work. I can actually hear air sucking if I hold the pedal just right.
That said, I want to replace both the master cylinder and booster.
Transmission has been shifting great, so seems it was just a fluke for now.
I'll start a new thread.