Agree with Barry here, I always suggest dino
oil on break in. We use Jo Gibbs break in
oil that is special formulated for new engines and break in.
You should have been able to look at the engine and tell if it had been run. I think they spin them or do a
oil pressure check and an air leak check on these engines. If they did not start it and go through a break in process and actually run the engine they would not have found this. I have had a few over the years that have had a ring seat problem and knew it pretty quick. Had to pull a few down and re-hone and install new rings. You can have a problem with anything so this is the reason we run them before we ship them out.
I hope you find something simple that will fix the problem. Do you have a lot of blow by, this is a sign that the rings are not sealed. You could just have an oil ring problem. Like Barry said a leak down or even a compression check is not much help. The easy thing would be if it is the seals. Does it ever get better under any conditions?
Thanks, Keith