That compression difference could be from valve adjustment, or the head needing re-torque...
Yup, seen them smoke out of the breather before from top end issues.. completely agree as a cause for smoke from the breather. When he mentioned foam, made me think more oil issue or bottom end. I've seen this on other engine platforms also when a feller bought Castrol GTX at Walmart for the oil change in their motor . The oil does not have polymers (similar to gear oil) for the gear mesh transmission. When the oil is compressed between the gear teeth, it breaks down and foams. (causes foaming and smoke from the breather). Or like I said, the friction modifiers in the oil are not wet clutch friendly. You can find more on that topic from other factory techs on BMW, Harley, Yamaha, Honda forums.. If you fill a rear end with regular motor oil instead of diffy oil, the rear will smoke out the breather too after a hard run.
I have been wrong before, the end result here will be interesting to find out... like I said before, if it were not having a foam line in the oil, I would say top end
~G~