How to find and fix roof leak in a flat roof covered with single ply

Flat roofs leak and sometimes you have to look under them to find whats happening, After inspecting the roof I decide to make some inspection holes through the old leaking roof materials and into the roof insulation the roof insulation is wet indicating that the roof is leaking however I don't know that the roof leak is where I'm working so I work backwards and make more holes in the roof until I find a dry area then I know the water was probably traveling down from that point I fix the roof as if Im using felt pages and overlay them using a sealant mastic. Leaking roofs with roof insulation under the membrane is know as a warm roof a good design in flat roofing however if the roof starts to leak then the insulation gets wet and getting it dry again is a difficult operation. It not unusual for us to have to completely replace the roof just because we cannot get the water out from within