The condition of the whole roof assembly and the cause of the fault, not the age of the covering, should determine whether to repair or replace. Before comparing costs, establish the water's path: it may travel along the membrane or flashing and appear far from the point of entry. Check whether the problem is limited and can be permanently removed, or whether it involves widespread corrosion, repeated leaks or damaged layers. Also distinguish a leak from condensation. A diagnosis from outside and from the accessible interior allows the scope of work to be matched to the actual cause.