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