Here is a pretty boring video (though perhaps my others ones are too) of the engine going in a circle for as long as it can. I got about 8 minutes 20 seconds. I have no idea how long it would run new but for me this is more than enough :-)
I have read they go 1/3 of a mile in a 10 minute run. Assuming that is true, losing 1 1/2 minutes isn’t bad for a ~55 year old toy. Heck it is hard for me to get to the mailbox and back in under 10 minutes! So I think the little roller is doing okay for its age :-D