I have the same problem. My solution is just to push down on the seat and squeeze all the water out of it before I sit down.

 

Day 1 after forcing about two minks worth of Mink Oil into the seams on the sporty's seat.

The weather cooperated and rained on the bike while I was cozy and dry at work. When I went out to go home, the seat surface was dry. I ran my hands along the seams, pushing down as I went. No moisture came out. I looked at my pants when I got home and didn't see the tell tale wet marks either. I also did a more thorough job of trying to squeeze the seams after I got home. Still no moisture. So far so good.

Now, I realize Mink Oil really isn't meant for sealing seams, but it's working so far. I'll probably end up trying a cloth seam sealant at some point.

 

Well, my experiment seems to have paid off. Three days of Debby raining on my bike while I was at work and I didn't get the wet streaks from the seams. I still think I'll get some seam sealant eventually, but for now the Mink oil seems to have worked.

 

Mine does this. I wish I would not have bought one. Does Mink Oil work?