I think all of them are like that...well at least these type.
I red flagged it on my PDI, and I think the dealer addressed it fairly well just as an effort to shut me up. Only did it on one of my slides though. Later I noticed it on the other slide too, and when I asked my local dealer (not the selling dealership) to fix it, after researching they refused pointing out that this is the way they come from the factory. I used to have it on my list of things to do, but never came accross a material to use and so it has fallen of the list....just hasn't been a known problem in our use.
Anyway, I can't find a picture and the thing is in storage, so....
basically what they did was take short pieces of the wiper seal used on the top and verticals ...that stuff that's maybe 3-4 inches wide...and screw a wiper flap the frame covering these two points under the slide. Not complete and perfect, but not bad in my thinking.... maybe you could run with that idea and improve on it.