The fourth answer makes the most sense. Someday, I hope all car and truck manufactures will build separate transmission oil coolers rather depending on 195 degree engine coolant to lower the temperature of a very small oil coolant tank inside the radiator expansion tank.
This design has got to be the most inefficient ways to lower the temperature of the automatic transmission fluid.Oil in cooling water?
Is more and likely transmission oil, why I say this, is because, most companies put the transmission oil cooler inside the radiators coolant tank on the radiator. If it develops a leak, and such, that is how you would know that there is a problem. It can be by passed, just get another oil cooler, and route the transmission oil lines to it.
it,s probably coming from where the transmission lines are hooked up to. there,s probably a crack in the radiator cooling part for the transmission. check the transmission to see if it,s low.
it is most likely your oil cooler the oil filter is attached to it possible just the gasket for the oil cooler but most likely the oil cooler itself.
cracked block blown head gasket head gasket blown between the cyl and a water jacket
Check the radiator to see if the cooler tank has a crack in it.