As I understand whether old or new house, there's a warranty period for leakage for at least 10 years.
However after 10 years, I think the unit below and the unit above need to co-share the cost. In this case, should be HDB if you are living highest.
One thing you can try is to check with a qualified surveyor before engaging him for a report. Structural problems should be handled by developer. Cracks due to earth settlement after 10 years should be individual unit's concern before take over.