Hi Kynan, and a warm welcome to the forum. Its great to have another Scott Bonnar owner on board.
Unfortunately Jocks has not visited the forum since late last year, perhaps send him a PM or email.
Re: your question on the ring gear, this is not the correct forum for questions on your SB590....I will move this thread to: Repairs and Maintenance >>Scott Bonnar Cylinder Mowers.
I will answer your question there....this keeps the archives intact for future reference.
I will now close this thread.