They ALL have this problem after a little riding. This is what I did and it seems to have fixed the water fall problem.
1) remove the loose silicone from around the rear heat exchanger
2) remove the piece of foam in the center rib of the tunnel and throw it in the garbage. Replace it with a solid rubber piece cut just slightly oversize and jam it in the rib.
3) use a good quality silicone or stuff call 'Automotive Goop' and seal ALL the seams and joints and around the rubber piece in the tunnel center. Don't be afraid to use the silicone.
4) put a 1" wide x 1/2" thick piece of truck cap foam down the entire each side of the tunnel and in the back where the rear bumper goes under the seat. Keep the end gaps on the foam tight so it doesn't leak.
Problem should be solved. I did this last year and it seemed to do the trick. No more leaks and no more water falls. You will still get an iced running board if you are riding in powder because the powder hits the side exchanger, melts and then refreezes to the tunnel if it is cold enough.
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