you have to remove this oily substance. Nothing will stick as long as this is on the fireplace. If you tried Muratic acid and this did not work, well, you have just used the chemical of choice. you need and must remove the oil.
Once you have done so, I would recommend using a good primer like Zinzer BIN or Bullseye. Apply several coats and let them dry thouroughly before the next coat.
For the finish coat I would use a good brand of paint purchased in a Paint Speciality store only, not in a home center. use a good water based paint in semi gloss. Apply several coats of this.
I do about four of these each month and its really easy once you get the hang of it.