Agreed this is a d!&% move on the part of the employer, but we don't know if this employee was a jerk and "had it coming." Maybe he gave the boss' truck an oil change on the interior before he left. I think there's more to this story.
This employee should go buy a key date penny and claim he found it in this mess, stick it to the man!!!
There's probably more to the story, but it's still a childish move on the part of the employer. Just try showing up with a wheelbarrow full of oily pennies and trying to buy something with them. A business would refuse to accept them. This guy should keep track of his time invested in cleaning and rolling and send an inflated bill to the employer for time and materials.
Related,
https://www.upi.com/Odd_News/2017/0...mpt-to-pay-270-fine-in-pennies/2221496853466/