Oil spray whether used or new a big NO! NO!. Get it serviced, the water is already oily thanks to their careless behavior, get the greasing parts greased and always get the body waxed after every wash, it will definitely improve the life of the car's paint and look nice and shiny too. Moreover don't let them wash the engine with kerosene or any other oil, simply clean it with water spray and surf, and if they have steam wash facility get steam washed, the best. Then Enjoy the ride of a nice, shiny clean car.