Roof peak - Interior leak

Our house in central Pennsylvania is a six-year-old entirely timberframe dwelling. We love it , but are have a problem with an interior drip on the north side in our loft area that appears to come from the roof ridge. We used vented stressed skin panels for our roof - OSB, styrofoam, drywall combo. The drywall has cracked from the peak down past the second purlin to the third. We have also noticed that in the summer, the outside roof (shingled) will buckle slightly from peak to drip edge along what appears to be close to the same area/line. The panels were splined together. We do not think that condensation is the issue, as I believe there would be problems elsewhere. We are careful of humidity levels and run the air exchanger faithfully. I am particularly concerned about the second purlin down from the peak developing a water rot spot. We are also concerned that we will have to remove the entire north side of the roof to check it out. Has anyone had experience with similar problems? And does anyone know any roofers who might have experience with stressed skin panels. As is typical, we had a very small, and not all local, work crew, including ourselves. We used conventional roofers to shingle it. Our project manager is baffled, he had thought it was due to a vent pipe condensation or lack of sealing around it. But we have addressed that - to no avail.
Possibly a spline was missed? Any suggestions or musings would be greatly appreciated. Thanks.

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.