The “oil slick” would be from the kerosene based jet fuel, not from the engine lubricating oil. There isn’t enough engine oil to make a substantial oil slick.
The kerosene oil slick would evaporate in a few hours. It would no longer exist.
If the aircraft broke up, for whatever reason, at 35K feet, there would likely be no “oil slick” at all due to dispersion and evaporation from that height.
Put both of your posts together, and it seems you are both right. The kerosine slicks were gone hours later.