are the seals coming out like they are supposed too?- I would go out next time it rains and see if you can track where the water is coming from. we had a seal on the top of the slide that would roll inn- not much about 8" it would run down and leak water at the base of the slide
the channel is for the slide to go in and out on- any cables on the outside?
I have read where some put some caulk where the seal meets the track causing the water to hit the caulk and not run past the seal-
they marked the seal where it met the top of the track, moved the slide out in and put the caulk there- let it dry and ran the slide out back out.
just a guess!
a picture would also help if possible