My A128 also leaked at the rear window. I took it back to the dealer and they applied the 3M Extreme Tape over all the rivets and rear window seams. I think it's fixed. I also talked to the Dealer and he said they have had trouble with sealing of those windows. They now seal under the window as well as caulking. They don't use rivets now. None of which does us any good.
The 3M tape looks pretty good and I think the problem is solved at least until the tape deteriorates.
The Tape is the 3M Extreme Sealing Tape 4412N, Acrylic Pressure Sensitive Adhesive, 2.5" Wide. It covers the rivets and seams pretty well. I also bought a roll at Amazon for $114 for an 18 yard roll just in case the fan ventilator leaks.