More concrete problems for a landlord in South Troy: One of my tenants changed the oil on his Harley in the middle of the concrete driveway; needless to say, he was the sloppiest thing on two feet. I do not know how long the oil stains have been there, but the tenant was there for 5 years, so I assume that some are at least that old.
Mac says: There are a number of products that are on the market, but the old timers used this one for old oil stains: saturate the stained area with kerosene or paint thinner and cover it with kitty litter. Leave it overnight and sweep it away. You may have to repeat several times and use new kitty litter each time.