grease monkeys
Can't speak for the poster who came up with 'greased monkeys' (and I wouldn't want to anyway), but the expression 'grease monkey' is old American slang for 'mechanic'. It was usually used for car mechanics, though I suppose airplane mechanics may have borne the nickname too. It was mildly derogatory, without quite reaching the category 'fighting words'. 'Grease monkey' bore no racial or ethnic connotations whatever.