Well, I found the problem and it was plain as day. The vents for the toilets never got fully enclosed by shingles. When I got the roof replaced in 2009, I found out in the breach that the actual contractors were a fly-by-night operation. As they were finishing, they had a big, blue tarp on the edges of the roof to collect nails. But then instead of actually carefully picking them up and dumping in the dumpster just feet, they dumped them in the grass directly under the roof edge! I wanted to yell at them, but that would have been useless, they spoke no English. Their truck was registered in Tennessee and the trailer in Minnesota. They were long gone the day after dumping nails (I told the main contractor, a reputable person, but those roofers were gone). And since it was a mass-damage event, it was a sort of take anyone you can.
Obviously I am going to have to see about getting that shingling replaced and maybe check underneath, Honestly, it’s amazing it has taken this long for a problem. But I imagine that 17 years of wind, Sun, snow , ice have finally beaten up any sealing that was done (haphazardly) back in 2009.
Eric