I couldn't find how to fix a leaking sunroof on a 2006 Toyota Highlander

Last Thursday, during a brief but heavy afternoon thunderstorm in Durham, NC, our passenger's seat and footwell was soaked, with standing water visible on the carpet. This happened once before, and Toyota fixed it, and it has also happened with our 2002 Jetta. We dried out the car with a wet dry vac and some ShamWow's (no kidding), and then parked it in the garage until we could investigate the leak.

The car is out of warranty, so we did not want to take it back to the dealer. I looked, but couldn't find, much information about how to check the sunroof or the drains. I did find some peripheral information - an illustrated manual that includes some headliner removal info here:http://www.toyotapart.com/installation/PT374-48020.pdf. This was very helpful.

This sunroof is not meant to be watertight, but features a drain system in all four corners, in which water is channeled through the pillars out to the ground. This photo shows where the hole is located, though you can't actually see the hole itself:

Our car also came with a sunroof visor, which is mounted using two moveable clips that clip through gasket where the sunroof meets the roof. I speculated that the drain system had become clogged or unplugged, but I didn't want to just stick a coathanger down there for fear of puncturing something. I decided to remove the headliner, which involved, in this order:

1. Remove handle above passenger door, easily done with a screwdriver:

2. Remove sun visor, also easily done with a screwdriver:

3. You may also need to partially loosen the clip that holds the loose end of the visor by gently twisting and pulling it out.

4. Now you need to remove most of the weatherstripping around the door, as this holds the headliner in place.

5. Using a screwdriver or similar tool (I actually used those free paint can/opener/bottle opener tools they give you at Home Depot), gently pry up the plastic footplate thing at the base of the door. You don't need to pull it all the way off, just far enough to begin pulling off the weatherstripping.

6. You also need to remove the plastic plate covering the pillar. I used the same tool and just pulled gently enough so as not to break any plastic.

7. Once those are removed, begin pulling out the weatherstripping starting at the base, then moving to the front of the car. I went all the way across the top, then left it connected on the backside of the door frame.

8. Now you can pull the headliner down a bit and see where the drain line connects to the sunroof drain hole.

9. You can also see where the line runs within the pillar here:

10. The drain line is threaded through the pillar and drains under the car behind the tire. Except for the tape holding the line to the pillar, it was not attached farther down, so I was able to pull it out and inspect the whole line.

11. After pouring water down the line, I was unable to locate any leaks or blockages, so my eventual diagnosis is currently just speculative.

I *think* the sunroof leaked because the car was parked facing downhill, with the right front wheel at the lowest point. This caused the heavy rain to pool behind the water tight sunroof visor rather than run off the roof down the windshield. The pooling water poured into the sunroof at a faster rate than the single right-front drain was able to carry it away. It spilled over the channel into the headliner and ran down to the pillar, where it dripped and soaked the seat. The other 3 drains were ineffective because of the angle at which the car was parked.

Does anyone with more expertise think that sounds plausible? We've removed the sunroof visor to see if that makes a difference. We're still uncertain, because the car had been parked in the same place for many strong storms without this happening.