I don´t think it is reasonable to have a renter waste precious vacation time in a foreign city to change the oil on the car he has rented. Something very similar is what happened to us. After renting a car from Europcar in Berlin and driving to Budapest, a warning sign came on the dashboard saying that the car ignition would be disabled unless we added AdBlue to the car before a certain amount of kilometers. We wasted significant time from our vacation looking for a place to get the additive, and finally had to take the car into an Audi service shop (Smoliner) in Vienna at the recommendation of the Vienna Europcar agency, a process for which we had to wait two hours.
This in addition to time figuring out what the heck AdBlue was, and significant time wasted searching for a location that sells it in Hungary with no luck, where after being told by the Europcar agency in Budapest that it was readily available, the service stations had no idea what we were talking about when we asked them if they sold AdBlue. We did our part as the contract says, and contacted the Europcar agency in Budapest and Vienna first. This is something that Europcar should check and refill before allowing the car on the road and not pass the burden along to the customer, especially without any advance warning. In addition, the rental personnel at the Heidelberg office where we returned the car were very rude about this when we pointed it out to them, and a supervisor in Berlin, Mr. Kuhne, said by telephone that we we were "way out of line" for complaining. I would have expected them to offer a partial refund for the time taken from our vacation to compensate for the trouble. Quite the contrary, they treated us badly on top of everything!