[GhostBella]

As a qualified Animal behaviourist im going to give you my opinion. The one thing I picked up on is that you said 'he's slightly calmer but still does it' now in my eyes if it was all neurological the behaviour would stay the same but would usually get worse with other noticeable repetitive behaviours, I think its phycological! Hes probably been kept in a tiny cage his whole life with no wheel or outside cage playtime and running round in circles is what hes had to do to exercise and has now become a habit. Defiantly get a bigger cage with more levels but beware that if hes been kept in a tiny space suddenly putting him in a large one might stress him. It would be like a human thats been kept in one room there whole life and never been outside of it, yes they would be miserable but suddenly rescuing them and bringing them out for the first time would be overwhelming and hard to cope with. Whether its good or bad thats all hes known and to suddenly have lots of space will be scary and daunting for him.
What I advise is that If you can get hold of or borrow a slightly bigger cage but not as big as what he should be in swop him to it and gradually move him up into a big size cage. If not keep him in the cage hes now and let him get used to it and used to using his wheel etc, remember hes probably never seen one. Iv watched the video and im 99.99999% its not neurological its behavioural and due to the reason above I can see him stop circling go to his wheel, get out circle again about 4 times round then stop look at the camera, circle again but slower then stop again. He can control it and is aware hes doing it, defiantly bad habit . He might never completely break the habit as its to deep set. The more stimuli hes got, the more he uses the wheel it will gradually get less and less but probably not go completly.