What part has disintegrated?
Mine also failed. The auto elec told me they didn't exist and I really had a 12V starter. When I plonked it in front of him he was genuinely surprised. Anyway, he dismantled it and told me which parts I needed. I sourced the parts, he rebuilt it and happy days.
So, can it be rebuilt? This might be easier than sourcing a new or s/h one.