We had a difficult to diagnose rain leak from the back cabin roof surrounding the slide area.
Turned out to be most likely due to the slide rails being made of wood, with a different expansion rate to the steel cabin top.
Over the years, this and deterioration of the sealant allowed rain to seep under the timber rails, probably via the two small drainage channels that prevented rain from pooling between the rails.
Water then found its way down the rail fixing holes into the back cabin.
Sarah at Glascote advised replacing the wooden rails with steel ones - this has been done recently, but has not yet been tested - but I’m quietly confident ?