Solihull: Garage roof leaking (ended)

Garage roof leaking

I live in a flat with a seperate garage in a block of garages. I paid someone to come and re-proof the roof, but water is still dripping through. I think he used "black jack" on it but he has now put 2 coats on and there is still a small bit leaking through. It looks as though it is washing off. I have given up on this bloke for not being reliable. The roof is corregated asbestos cement. Is there a way to re-proof permamently this or would the roof need replacing? Quotes for which ever is recommended. Thanks
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