Jerry,
1: Yes, they are indeed. Often it's not the slide that is leaking, it's the wall that holds the slide out there.
2: As you suspect, the roof on the slide has likely stripped away from the walls, and as the roof sags and fills with water, the edges can fail. Slide roofs do help with this, but often to cut costs, they install a roof covering the same length as the slide, rather than the maximum past each edge they can install. If you are installing aftermarket, put the brackets out so the slide coverage extends as far as possible past each wall. Builders, we look for your best effort to keep us happy, and will reward you with increased business if you outperform the market in water intrusion prevention.