A few weeks ago I was asking about being reimbursed for a quart of oil / the ethics of taking care of a car that isn’t yours.
Well today I dropped off the car and company XYZ had absolutely NO problem reimbursing me cash on the spot for the quart of oil.
Sometimes it does pay to do the right thing (even though in this case i only broke even 
)
I’m certain that the rental company appreciated you maintaining the vehicle. I check the oil in rental vehicles if I drive them a long distance. In the first place, I don’t want to be stranded and secondly, I hate to see machinery (except lawnmowers) abused.
On the other extreme, my wife drove a van full of teenagers to a church work camp 500 miles away. THe church rented the van from “rent a wreck”. At the first gasoline stop, the minister checked the oil and decided it needed a quart, so a quart was added. The same thing occured at the next gasoline stop. Another quart was added. When they got to the camp, my wife was a little upset with the van, so she opened the hood and checked the oil. It was 2 quarts overfilled. She took the van to a service station and had 2 quarts or so drained out so that the oil read where it was supposed to on the stick. Our minister had misread the dipstick. She paid for the service, and since the van ran fine, she didn’t say anything when it was returned. On the trip back, she checked the oil at each gasoline stop.
I kind of had a paranoid trip after adding oil to the car, because the Mazda owner’s manual didn’t specify if the oil being at the lower mark is a full quart loss or not, however common sense told me that pretty much every production car is calibrated for the lower mark to read one quart, correct me if I’m wrong.