"Braking action "poor"data reflects runways covered with wet ice"(JAROPS/FAA/BOEING).Nothing about oil.To land on a runway covered with oil would be beyond the scope of your performance manual and braking action reports at best subjective.
Furthermore,Friction Coefficient/Braking action is given as a two figure group(ie 91=poor) and percentage of runway contaminated.
Not as (poor/poor/poor).Only RVR is given as such depending on the no of Transmissometers.
Runway state is only given in Metars/Specis and sometimes ATIS ie Frankfurt)
NOT TAFs,you cannot predict present runway state.
If you ever get to fly a big jet doubtful any operator will let you land less than Braking action Medium even at CDG!