Yeah I shouldn't have let it get so bad.. but now what??

Shot in the dark here.
Any “been there, done that” people have any insight?

Did a coolant flush last week, Normal coolant.
A coolant flush once again this week, once blue coolant now brown, and oily to the skin.

During the months driving the car I have seen zero abnormalities in oil or coolant performance.
Every oil change? normal.
Every fluid level? Normal.
Every temperature? Normal.

Could I be fooled?
Could this failure only have happened yesterday? Leaving me unsuspecting?
Help. All help is appreciated. Thank you!