On 10/3/2015 6:27 PM, Ken wrote:

In addition to the advice others have given, look at the boots around stack
vents. I had a leak that only showed up during excessive rain due to the stack
vent having dropped slightly in the attic. That caused a dimple to form around
the stack vent boot and it caused water to accumulate in that dimple. It was
easy to understand once it was found, but not at all obvious while searching
for it.

Each year, I examine our roof for "problem areas". We have:
- vent stacks for kitchen and two bathrooms
- exhaust fans for kitchen and bathrooms
- water heater and furnace exhaust
- water heater and furnace combustion reliefs
- several "wire entries" (CATV to interior walls)
- downdraft cooler air inlet
- water line for swamp cooler
- 220VAC supply for cooler plus "signal control"
- a few skylights
- 6 or 8 large "roof vents" on the high side (flat roof) of the roof

I.e., we have lots of places where the roof has been intentionally
perforated. Each of these represents an opportunity for a leak
to develop.

Many years ago, after watching problems neighbors were FREQUENTLY
having (often being conned into replacing their entire roofs!),
I learned that *removing* much of the old "patch"/sealant in each
of these places BEFORE applying "new" leads to greater roof
integrity.

But, it's a fair bit of work -- the "patch" compound isn't designed
to come *off* easily! :-/