Disclaimer 1: Not sure if 986s have this issue, but it's prevalent with 987s.
Disclaimer 2: I did not come up with this idea. Rrunkle on Planet 9 did but I've added some detail and updates to it. Since I did not find a thread on this topic on 986forum, thought I'd pass it along to the membership. Plus I've swiped a cpl pics that I didn't take but need to assist with this thread.
The Problem: In Porsche's infinite wisdom, they use strings and elastic bands to keep their convertible tops in the proper position. Not good from a longevity stand point as both stretch over time and cause issues. When the elastic band stretches, it allows the canvas to go over the outside of the top bow, putting a lot of strain on the stitching holding the beading edge of the canvas roof. And once the canvas goes over the outside of the bow, the elastic band is stretched further and it will always go on the outside.
Make shift solutions: Stop the process of putting the top up just past service mode and get out and guide the top over both bows. Or you and the significant other reach back while the top is going up and guide the canvas inside the bow. Or I've heard you can push the top of the back window up and out which tucks the sides in enough to go inside of the bows. This doesn't work well if you have a windstop.
Solution 1: The elastic band has slots in it which allow you to tighten up the band. It requires a torx 15 socket. The first step is to release 2 Velcro straps that keep the headliner on the framework. This allows you to get inside the top. See the circles for the Velcro locations.
The elastic band torx screw is about 8" into the bowels of the top.
IMPORTANT: before removing the screw, put a towel into the compartment so if you drop the screw it doesn't fall into oblivion. Be sure the towel goes all the way out the window (you might get the screw out but drop it before you get it completely out - voice of experience). And don't forget to pull the towel out after you're finished.
Once you have the screw removed, the strap w/ elastic band looks like this.
Try moving the screw into a closer slot (like the arrow points to in the above pic).
HOWEVER, it is important not to make the band too tight as it will snap if there's too much tension on it. The problem is that band becomes less elastic as it ages and stretches, so you may find yourself between slots (too loose doesn't fix the problem, too tight breaks the band). What to do then?
Solution 2: Connect some bungee chord (aka shock chord) to the strap and use it instead of the elastic band. Here are the steps to perform this solution.
A. Buy some bungee chord at a local hobby store. I got mine at Hobby Lobby.
B. Cut a 12" section and burn the edges to prevent fraying.
C. Fish the looped chord thru the strap with a thin wire.
D. Measure 4 1/2" from the gray strap to the end of the loop. My measurement was with the loop pinched at the end (it's not pinched in the pic).
UPDATE: I've had better luck with 4 1/4".
Take a safety pin and pierce the strap, both pieces of chord, and the other side of the strap. Put the pin on the elastic band side of the strap since that's the side of the strap that's away from the canvas top. It may take a couple of attempts to get everything pinned properly.
E. I removed the small washer on the torx screw and replaced it with a 1" washer (10x1" shown or 1/8" x 1"). This gave the chord something to slip over yet have enough room to stay in place when tension is relaxed (top down). Others have simply tightened the chord down with the torx screw. I prefer my method as it allows me to keep the torx screw completely tightened as it was meant to be. - don't want it coming loose and falling out.
Worked great after several days. I may go back and hand sew the chord to the strap for added strength.
