Removing factory silicone sealant

You need to use something abrasive to clean as much silicone off as possible and then flush it and do it again. It's pretty much impossible to completely remove the silicone contamination. I'm a silicone hater; however, the flowable silicone Winnie uses is very good stuff. When I replaced the skylight with a fantastic fan on my Winnie about a dozen years ago, I abrasively cleaned the roof surface and sealed the fan with the Winnie silicone.