All bucket seats fill up with water if water are left on / in the seat.
It's not a defect, leather is not waterproof.
I don't know about that. The leather on my body is pretty good at keeping fluids in that are supposed to be in, and other fluids out that are supposed to be out. I can stand in a shower for what seems like an hour, or soak in a tub, and I don't gain an ounce. So obviously my body isn't soaking up any water.
The leather insert on a new seat should not allow enough moisture through to saturate the foam inside. And of course the rest of the seat is vinyl so that shouldn't absorb water either. The actual stitching is supposed to be treated for water resistance, but that might be the weak point of the entire thing. If water is allowed to sit in the bucket of the seat for an extended period of time perhaps enough could get through to soak the foam, but I've never had that happen on my CVO seat and it's nine years old and has been caught out in a few rainstorms.
jimcb1, does water bead up on the seat or does it visibly soak into the seat? If the materials were treated properly, the water should bead up. If the foam is actually saturated with water, that is definitely NOT normal.
Jerry