90hp Merc. 4-Stroke Water in oil --Diagnosis?

[frustratedboater]

I have a Merc. 2004, 90hp, 4-Stroke outboard that is getting water in the oil. I know that there are only a few ways it could be entering. I have already, split the mid-section and replaced the water tube grommet and all that is associated, both mid-section gaskets, etc. I started it up and ran nice then started seeing the oil getting opaque and slightly milky. I wasn't happy...
What would be the best way to determine if it was the head gasket afterall? Leakdown? Could it be something else that I'm not thinking?
Can I replace the head gasket on the motor without splitting the powerhead from the midsection?

 

[frustratedboater]

Anyone??

 

[airshot]

Looks like rust on plug ends !! Water in cylinders ?? Compression check needed.