repairing old tracks is not recommended here. there are stories of people running there old tracks without track armor and being impaled by the steering column when a track has broken, hitting them in the back. even if you have your track armor there is still a potential danger especially if you run them fast.
that being said there is a way to repair them for use as a display or very low speeds. mostly i have seen this done on the farm halftracks.
take a chain and weld the links to the outer edge of the bars of your tracks both inside and outside. make sure the bar spacing stays even through the brake and there is no slack in the chain.
again these old tracks can be dangerous and this is not recommended.