1st question is why one would remove the lovely patina- 70 years is probably an optimum capillary saturation cycle for unglazed brick- leave it alone & by 2070 the oil will probably have turned around like bell bottoms, child molester goatees & tattoos. First, I think I'd consider putting yesterday's coffee in a spray bottle and trying to get the wall from 3 ft up to match the lower section & I am serious about using coffee on brick to "age" it as I have, twice, successfully used it. But if I had to get the oil off- my first try would involve a 5# box of granular/dry Tide to which I would add mere ounces of water at a time until I had a consistency that could trowel onto the wall & then just leave it alone for a few days & see what happens when you knock it off w/ a stiff brush- you don't want to hose it off... what are you going to do w/ the contaminated water. I know it's worked on my driveway. DD -- We have enough laws on the book, already, to confound us well into the 21st Century