Milky transmission oil/ Year of my tractor

As far as the serial number, it should be on the left side of the engine, just under the head. You may have to take a wire brush and clean off the area. I know the 9N I looked at at our fair today was hard to see.

The milky color of your transmission fluid is definately water. Unless the tractor has been sitting for a very long time I doubt whether it is condensation. It's more likly water that has entered the case through the shifter boot. Water from a cracked block would not be able to enter the trans/rear-end housings. Your engine oil would be milky in that instance. However, someone else may have other thoughts. I hope this helps.

2. I seriously doubt if the oil could ever get enough condensation to turn milky. Lighten up, get contaminated where you can tell there is a problem, yes. Maaaaybe after years of total neglect, no oil changes and running without a thermostat. The engine must get warm and stay warm for a while to boil the moisture out of the oil. It is not uncommon to see the oil filler area coated with white milky looking stuff if the engine never warms up. You mentioned the driveline oil in your first paragraph and then you talk about the block in the last sentence. Are you getting a milky color in both or do I misunderstand? A cracked block could give you milky crankcase oil but not drive train oil. If your drivetrain oil is getting milky after a change of oil you are probably getting water intrusion somewhere; shift boot lift arms, seat mount spring, or control spring shaft. When you changed the drivtrain oil did you remove all three drain plugs? Get all the old oil out?
I am in the deep south and we have a some days where the tractors will sweat to the point of water dripping from them. I have never had any milky looking oil. My tractors all stay under cover.
Some will probably disagree with me about condensation causing milky oil but I just don't think there is enough volume of moisture laden air in a drivetrain area to condense enough water to turn the lubrication milky.
If you have a three speed tranny you have 9N or 2N. Hope this helps.

ray