Glad I stumbled across this post. I've just bought my car and have the exact same fault with the stitching at the top of my rear plastic window. Saw it before I bought the car and decided it wasn't a deal breaker though the heavy rain we're currently experiencing is managing to find a way through. I see no reason why the existing holes in the plastic cannot be re-threaded and tensioned to the hood with some quality cotton thread and I fully intend to have a go at this myself... when it stops raining. As a side note I've noticed that the plastic rear screen gets tensioned in the middle top area whenever the roof is put half way down to perform the 'boxster chop' so it's of no surprise that the stitching comes adrift in this area.
Had to laugh last night, I jumped up from my seat in front of the telly to the awful sound of the horn and alarm on the car. Ran outside expecting to have a rumble with some rascal breaking in to the motor and was relieved to find that the towel I've balanced on the wind deflector to catch the drips had dropped onto the seats triggering the motion sensors!
