Here a little story. I had one of the 99 Miata that needed a new engine, thrust bearing issue. Actually it had no issue but the idiot dealer did not know how to check endplay and in the end I got a new mazda engine. The car had 30 days left on the warranty I had owned it 4 days so I ran it to the dealer to cover my asssss with this thrust bearing issue.
In the end I was trying to verify if they rebuilt an engine or it was new. I get it home and pull a spark plug and see RUST on the piston top and very very slight on cyldinder walls. I drove it about 2 miles. I storm back to the dealer telling them they jacked and they showed the bill from Mazda USA, shipping paper work blah blah blah. I go on their showroom open the hood of a new Miata, take out a spark plug as they watch and bang, rust everywhere, LOL!!!!!!!
I ask to see the old engine and I check the end play just to be a smart assss and it is .006" well within spec. I tell the mechanic you just replaced an engine for nothing. He mounted the dial indicator on the sway bar and pushed in the cluch, idiot checked the free play in the motor mounts and everything else. I checked the "new" engine which was not easy and it was .008" LOL.
Bottom line I have seen more rust in two new engines than I ever though possible. Sold the car years later and never burned a drop of
oil between 5 k
oil changes.