Looks like nobody wanted to touch this one.

It sounds like your problem has less to do with panels than with roofing.

I recommend that you buy a square of matching shingles, dust off your ladders and safety gear, and spend a few spring afternoons up on the roof ripping off those shingles around the area of infection.

If you can't see any obvious signs of defect, cover the offending area with one of those fabulous self-adhesive, self-healing asphalt membranes sold under several trade names.