Starting a new thread on this, as I want to bring this to anyone's attention who has or will experience something similar.
In a nutshell, about a month ago, my AWD in my 2008 stopped working. It happened to coincide with a massive rainstorm that happened non-stop for days. Interestingly enough, after the storm was done and things dried up the error went away but came and went from time to time. When it rained it always came back.
I brought it to my mechanic who scanned the code and found it was a AWD relay. In looking at it, he found the relay in the back fuse box (rear left side, against the wall behind the carpeted cover). When he opened the cover, the whole area of the fusebox was corroded and the relay was as well. He replaced the relay and cleaned up the corrosion. He did say that obviously moisture got into there at some point but hard to say when and how long. Due to time I opted not to have him figure it out and I would do it myself. In looking online, there were reports of issues of the tailgate harness letting water in, so I basically sealed up anything I could on the side wall of the frame of the tailgate area with silicone. Looked ugly as can be but who cares - that whole area was one big silicone glob.
Had my daughter jump into the trunk and I went to pour water on the side of that tailgate with it closed. No water got in. I assumed that the problem was fixed.
This morning it is raining HARD again. I was like, "yeah well, who cares - my car is nice and dry now." I opened up the cover for the fusebox and to my surprise, there was water in there again. It is coming from the INSIDE of the carpeted wall and dripping onto the fusebox. I have no idea from where it is actually coming from on the outside. But based on the fact that the tailgate was closed all night and morning, no way it is leaking through anything on the tailgate side (which is all globbed with silicone anyway). But since it was raining hard and I didn't want that fusebox getting wet, I stuffed a bunch of hand towels in the space above the fusebox (see photo). I checked it later this afternoon and the towels were drenched. I can only imagine how much water got into the car when it rained before I discovered this (which makes me kind of thankful that that AWD error came up initially).
Called my mechanic to make an appointment but in the meantime I talked with one of our vendor colleagues. He suggested I talk to another guy at work who has a 2010 MDX. So I went up to the other guy and asked him whether he has had leaking. To my surprise, he emphatically said YES. Not only did he have leaking, but it was leaking in the same area, and it was a lot worse than mine as he showed me videos of water coming into his car from the carpeted wall seam - at least it wasn't dripping on his fusebox as the water came in about 8" in front of where mine was, but his was pretty bad - it looks like a dripping faucet on the inside of his car. He said that he called Acura and they asked if he had a roof rack. He said yes, and they said it is leaking from there. How Acura knew this, I don't know...but my colleague decided to tackle the job himself, figured out how to remove the roof rack and then apply tons of silicone to it in order to stop the leak. He said it has stopped the leak completely since then. So on a coffee break this afternoon (a long one), we took my car out of the rain and parked it in one of the covered areas at work, and I pulled out the silicone tube and he went to work disassembling my roof rack (I offered to do it but no point having him explain it to me when he can just do it since he has more mechanical aptitude than I), globbing silicone on the 6 x bolt areas (3 pairs of 2) that held the rack in place - and then screwing everything back. I was pretty amazed that there is no rubber gasket or anything between the roof rack bolts and the roof rack. I can see how water would get into those holes. Hopefully the silicone did the trick.
So now it is a waiting game. With the roof rack out of the equation, if it continues to leak, my next thing to look at it would be the rear fixed window. Hopefully that's not the case. But we'll see.