Oil in Coolant Tank.

I don't know if it is engine oil or ATF. How do I know if it is ATF and it is due to Valeo Radiator issue.
I try to find if it is Valeo Radiator or Behr, but I could not find the marking or label on Radiator.
Please can some one tell me where I need to look for label or marking for Valeo or Behr Radiator. Is marking on top of Radiator or bottom or driver side or passenger side.






Thats not good!. If you are sure no one poured oil into the wrong place:
Get a test kit to check for combustion by-products in the coolant. This will tell you if you have a blown head gasket.
Take a sample of transmission fluid & have it checked for glycol.
Good luck!
Wipe your oily finger on white paper,.... transmission oil usually have a bit of a reddish tint to it,... ok, not the most scientific method.
New ATF (Fuch Titan 4134) was clear reddish colour.

C230 Sport C is right - sometimes the red fluid ends up looking like this.






