190 water in oil saga continues

"Will pressure testing also point to a head gasket problem ? Or is that not an issue for water in oil?"

In some extreme cases, yes, but generally a head gasket problem will lead to a poor running engine with combustion products forced into the cooling system (oily black coolant, etc.) Compression pressure always overcomes coolant pressure and leads to coolant being blown out of the overflow. Very seldom will a head gasket seep water into the cylinder.

Paul

"Question: If rain had gotten into the exhaust stack would that end up in the oil? Also will the liners leak just sitting there?"

Sure rain could do it, IF it sat out long enough. 1" of rain in that 3" pipe would be about 7 cu in of water, hardly enough to fill the horizontal muffler on a 190 to the point of overflowing into the engine. You also would have had a sticky carbon mess out of the pipe when you started the tractor.

If there is only a small leak in the liner or o-rings, you may have to pressurize the cooling system to make it leak. Buy or rent (Auto Zone) a cooling system tester and pressurize to 15 lbs with the pan off and watch for leaks.

Paul