Hmmm Bob, Frank, there are a couple of ways to read the original post.
I do not have any idea if I understood it correctly, but this is what I was reading.
Let's say I work for a big company (just so happens I do) and my boss, (very much not the owner of the company) tells me to pull his truck into the shop and work on his personal vehicle (not owned by the company) and just log it as work time..... Paid by the company.
We just had this come up with some city employees taking city equipment to the supervisors house and working on his driveway during "duty" hours.
So, put in another light,
Bob, I bet if your shop foreman, had one of your shop mechanics, working on the shop foreman's personal equipment on your dime, with your stuff and your equipment you would be a little less then pleased.
And to be honest, the mechanic is just in a CRAP position. He is going to catch heck no matter what he does, or where he turns. If he does it and get's caught, he is in the crud with management. If he turns in the worthless supervisor, it becomes a his word (subordinates) against a long established supervisor's (who may write his eval's) and management may or may not believe him. And at the least the other guys in the shop will not exactly trust him fully if he "rats out" the supervisor, particularly if others in the shop had been doing it in the past and get dragged into the fray.
Personally, I think the mechanic handled it about as well as could be done. Took himself out of the Foreman's line of fire, Foreman is not going to ask him to do anything again, he did not "rat out" anyone (whatever your perception of that is, and just using the term as it is commonly accepted) and it is not like the foreman will go complain to management that the mechanic did a poor job of servicing his personal truck on company time. And sounds like he did not even use any consumables, so hopefully he signed out early and did not open himself up to any theft charges if it all goes awry.
Then again, maybe I just read it all wrong.