If you have anything milky in your oil you need to find the cause and fix it. It only takes a tiny bit of water to destroy your engine, only a few table spoons in the pan will ruin your day.

If you have replaced the manifold gaskets (the most common cause) and found no sign of leakage and have no excessive signs of water usage (like a cracked head or head gasket) you may have a crack in the intake.

Cracks in aluminum are hard to see and often are not cracks at all but casting porosity in which water will migrate through what seems to be solid metal. Other common failures are cracks in the water passage that connects the heads. The crack can be small and actually open and close depending on engine temperature.

Use a dye penetrant to disclose the leak. Run the dye for a few hours or a day or two and take the manifold off. The dye will have fillowed the leak. It will be obvious.