The most common cause of this failure is from cutting away the covering where the stab will be glued. When you cut the covering you are also scoring the sheeting underneath. This is what GP will be looking for. I use a low temp soldering iron with a real small tip that melts away the covering rather than cut it. I'd look real close at the edge of the covering before cutting it up to send it to GP. If you can see any evidence of scoring GP probably won't replace it.
My $.02
basmntdweller