1998 Ford Explorer transmission and radiator

I had my transmission rebuilt previously and had a brand new radiator installed as well. After a few short days I noticed that there is a red oily type of fluid in the radiator as well as in the coolant tank where you put the antifreeze coolant. Ive taken the vehicle to atleast 5 diffrent repair shops in town and they all gave me 5 diffrent things on what I could be. I do know that the red oily fluid is transmission fluid but what I dont understand is why its in my radiator and in the radiator reserve tank. Can you please tell me what I can do. Or what you think it might be?