Well done, you certainly rack up the miles. My wife’s 2.5 year old has done 10300 miles ! It is interesting that you note the oil was at the top of the dipstick, which I also would have expected. However on my Mercedes, the oil is filled up to halfway . It has an electronic dipstick, and the oil is very carefully measured so not to go above that level. At first I thought I had low oil and was tempted to top up, but it did not use any oil and I was glad I checked as it could have damaged the engine or various emission components. It is serviced by a main agent.