I haven't replaced one personally, but had my dealer replace my horizontal wiper seal shortly after delivery due to an installation issue. If my TT was out of warranty I would have replaced the seal myself.
It's important that the wiper seal(s) when installed the slide's top two corners are closed (no opening)....., the horizontal seal overlapping the vertical seal. Also, the top horizontal wiper seal should be making contact fully along the slide roof surface..., the wiper seal will be at a slight angle when the slide is fully extended.
Before removing the old seal insure the correct replacement seal is available. Haven't checked, but there should be some DIY videos out there.
Bob
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2016 GM 2500HD 6.0L/4.10
2018 Jay Flight 24RBS
2002 GM 2500HD 6.0L/4:10 (retired)
2005 Jayco Eagle 278FBS (retired)
1999 Jayco Eagle 246FB (retired)
Reese HP Dual Cam (Strait-Line)