grease monkey
grease monkey {n.}, {slang}
1. A person who greases or works on machinery; a mechanic or worker in a garage or gasoline station.
Hey, grease monkey, fill up my gas tank!
The grease monkey was all dirty when he came out from under the car.
2. Airplane mechanic.
Jack was a grease monkey in the Air Force.
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Source: A Dictionary of American Idioms