I just got my first aftermarket seat (from Rich's in Kingston WA) in 38 years of BMW riding. It's just swell.
Stock seats have one-piece vinyl covers, which (if not punctured) are impervious to rain. The new seat is also covered in vinyl, but there are two sewn seams, with the resultant series of small needle holes. It doesn't rain a lot in Santa Cruz, and the bike lives in a garage...but I plan a long trip this fall, and I wonder if I should seal the seams (as I might a backpacking tent) or provide a rain cover for the seat when the bike is parked. I don't have any desire for a cover if one isn't needed to keep water off the seat.
What's your experience with this issue?