Instead of guessing where the leak is maybe you should actually find the leak. People have offered many suggestions for you to try and none worked. When they build new vehicles they all go through a water test to make sure they are not leaking anywhere. Get the hose out and get looking!
I would advise trying to rule out one problem at a time. Did you test your roof drains with water after you blew them out? I would guess it to be possible that although they may still be intact and air passes through without a problem that there may be a small leak in there some where.
Get the hose out on the hatch and TEST it for water seal. Sometimes a good visual inspection will not work.
Check the doors, check the rear window seal to make sure it is not leaking.
At this point you need to find the source of the problem and correct it before you lose your mind guessing.