There are lots of reasons for them to leak. After a rainstorm go outside and look behind the wiper seal and see if you can see water tracks. If you can follow them to the prblem. I found one trailer (King of the Road) where the molding strip had been installed with a slight upward angle to the ouside and allowed water to run in under the wiper seal. There is also the possibility that its not the slide thats leaking. I found one that had a leak in the roof just over the corner of the slide and everyone who had looked at it never checked the roof until I did. It could also be as simple as a slideout room adjustment is needed. A good tech might be able to help you. If you are set up and staying in it call a mobile service out. Check with your local parts store for a reputable one.