One of the things that comes to mind is that it could possibly be
antifreeze.  I head gasket problem doesn't seem to likely since one would
expect that to show up on paired cylinders, e.g., 1 & 2, not 1 & 4.
However, it could be that there's another source for antifreeze getting into
the engine such as a pinhole leak in the water jacket of the intake
manifold.  I had this happen to me on an older Honda.  Inspection of the
intake manifold revealed a streak of dried white antifreeze running down the
inside of one of the intake runners.  Pressure testing it showed that there
were air bubbles coming out.  I had good luck with a used manifold from a
wrecking yard but your mileage may vary.

Eric