Depending on your frequently the bore attachment to your tractor has been used, it might need replacing after a decade or after just a few years. It might also be that the owner of such a machine does not have permanent employees that are able to change parts on a heavy working machine. In either case, contact the people who offer local Bore Replacement Services. It is good to get back to work.
Bore bits can weigh many pounds and might also have a sharp edge. It might suspend by several attachments, and changing it without several people or a jack can be dangerous. Since it is a job that only needs to be done occasionally, having professionals do it can save a lot of trouble and avoid the risk of personal injury. The bit also has to be ordered and delivered, so it is best to let the experts complete the job.