Hi Sprocket, welcome to Outdoorking.

You probably know that the Scott Bonnar Models 430 and 590 are very similar (the belt clutch arrangements are probably the biggest difference). They both have a fairly serious weakness, in that the plastic gear which drives the rear roller is prone to coming loose on its steel hub, at which point there is no longer any drum drive. You can read full details about this problem, and how to deal with it, in this thread:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=22699&page=1

I suggest you read that thread, and then come back here with further questions.