If you can't trust them to simply drive it into the work bay properly how can you trust them to do something really complicated like doing an oil change??

Let's see...

"Hey Buck...does transmission fluid go in the radiator thing or in the hole that says OIL"?

"Neither stupid, it goes in the windshield washer squirt bottle thing."

"Oh...I already filled that up with antifreeze!"

"Nah...the antifreeze goes in the hole that says OIL."

"What'll I do with all this oil?"

"Put it in the radiator, stupid!"