His boss denied doing it, so I would demand a check for my back pay. If his boss admits to doing it, sue him for the cleanup costs of having oil and grease leak into your yard.
At what point was the oil and grease deliberately ruining the currency?
https://www.livescience.com/34286-legal-or-illegal-to-destroy-coins-paper-money.html
According to Title 18, Chapter 17 of the U.S. Code, which sets out crimes related to coins and currency, anyone who “alters, defaces, mutilates, impairs, diminishes, falsifies, scales, or lightens” coins can face fines or prison time.