Flat Roof Repair

We put a "rubber" roof on a house with a flat roof about 15 years ago. It has been leak free until I spotted a bad one in the bathroom after a really bad rain. I only have to climb up one story to look at the area where I thought the leak was coming from. I could find no damage in the covering, and no smoking gun as to where the water might be coming in. I did detect a VERY soft spot in the area above the leak. Is it wise to cut the roof in a 3 sided slice to uncover this area and replace the sub roof? If I do that, can I re seal that area by putting back the slice of rubber into some wet/dry roofing and be safe? Or does the repair HAVE to be done by a rubber roofing specialist. (I know this roof is old enough to be replaced, but no one will live there, and it is just not viable to put ten grand into a new one at this time. Comments appreciated as always!

 

I have no rubber roofing experience, but I would think a DIY patch repair as you described would be better than doing nothing. Possibly followed by a flood-coat of liquid rubber and mineral broadcast over the entire roof, both to hide the patch and buy some more time before having to spend the big bucks on a complete new installation.