This built up roof is close to 30 years old and is being replaced this coming summer. For more than the past ten years (going back to when it was under warranty), it has had leaks in a line along this area and a parallel line a few yards over.
We think these were tie-ins from when the roof was installed. They just were not laid right, and it was hidden under a thick flood coat. The one on the other side ended up taking an entire roll (3' x 33') and then some to finally get under control.
It doesn't help that water lays there, continually testing and weakening whatever patches we make. Both of these failures, however, seem to be faulty installation...exacerbated by ponding water (or melting snow...in this case).
Using an asphalt cement made for wet surfaces may have given better adhesion, but, since this patch only needed to last a few months before the entire roof was torn off, a cheaper product was used. Unfortunately, the GacoPatch that we applied the following day, after scraping and thoroughly drying this section of roof, cost more than premium cement would have. It should be able to handle the ponding water better and get us through until summer.
Unfortunately, the insulation is so saturated that, even if our newest patch is 100% watertight, residual water trapped within the layers of roof will get pushed out when everything expands on a nice hot sunny day and drip inside again. It's always fun to hear about an active roof leak when the sun is out...