I know things... A lot of things.
Join Date: Feb 2015
Motorcycle: GSXR 750 K4
Re: Milky oil window/filler cap
Was the oil milky when you flushed it? When the bike is used for small trips only and the engine doesn't have a chance to heat up the oil and remove dissolved water, the crankcase tends to be rich in water vapor, which condenses on the engine covers. There, the condensed water mixes with the oil film and makes it milky white. As this happens on the sight glass as well, it looks like the bulk of the oil is white, although that is only the case for a thin film, as explained.
I don't think condensation can saturate the oil with enough water to turn all the oil white (at least that was not the case with me this past winter, where the engine was subjected to small, daily trips to work, that barely got it up to temp). If that is the case, you probably have a leak somewhere allowing water to get into the oil. Besides the head gasket, I think that can also happen at the water pump, so some tests would be in order before arriving to any conclusions.