Help with 16520 case

[explorerdude]

Hey everyone, explorerdude here! Hope it’s alright to ask for this, could you take a look at this gen 16520 case I purchased and let me know your thoughts on whether it’s authentic?

It has definitely been polished, which I’m ok with, and the eBay seller seems to be trustworthy given his many sales of gen Rolex parts and good feedback. That being said the case shape has me asking myself some questions on whether it might be a aftermarket case with a custom serial. But again that could be because it was polished. Hope you’ll have some time to take a look, thank you!!