X5 E53 Rear Footwell Flooded with Water - Where is it coming from (Not the Doors)?

[minz-x5]

The dreaded water problem struck my car. Every time it rains, the rear-left footwell (behind the passenger seat) fills with water.

At first, I thought it could be the door vapor barrier, so I opened it and it was a little bit torn above so I fixed it. I tested it, no water came in. Next time it rained, water flooded the rear-right footwell, so I took it to BMW here in Mass. They said the sunroof drains were clogged, they cleaned them and charged me $130. It rained again and guess what; the floor behind the passenger seat was flooded...

After reading some forum posts, I opened the hood and cleaned the carbon filter area that had some leaves. It didn't do any good as next time it rained, water flooded the same right rear footwell.

I've blasted a hose over the entire car - including directly inside the rear quarter window, and came up empty handed - no water appeared inside.

Any suggestions before I take it to BMW again?