In major writes:

Had a recent motor oil quart slowly leek onto a ribbed concrete surface.
Not all of it leaked, but it left a slick about 2 feet in diameter. I
have tried to clean it up with materials I had on hand, mainly absorbing
as much as I could with potting soil and sand, then scrubbing the
remainder with Dawn dishwashing liquid solution, paper towels dipped
into that, and then I would scrub. Looks like I got most of it, but I
still see some remaining. Best way to remove that would be welcome.
Thanks.

The key is... time.

What I've done is taken Tide Laundry powder (others would probably
work as well, but that's what I had), wetted down the area, and
sprinked the detergent into it.

I'll keep it dampish for a couple of days, and then when I wash
it off (or ... if it rains.. ) 90 percent of the stain is gone.

Doing it a second time gets 90 percent of the remainder gone.

(Numbers for illustration).

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