Akin to grease monkey, it is used to primarily describe auto mechanics that specialize in routine maintenance, especially oil changes. Like grease monkey is can be used as both a derisive comment or to show camaraderie.
That damn oil ape doesn't know what kind of oil filter fits a 2007 Nissan Altima.
THAT was the worst customer my fellow oils apes and I have EVER had to endure. I'm glad I pissed in her oil filter...