I rebuilt my Warn myself and replaced the motor because it was corroded. I would be surprised if there was an electric motor out there that was sealed. I would imagine that they would need some sort of venting for cooling. It is always good practice to run your winch for a while after submerging it just to dry it out.
However when my Warn eventually does die I'll have a look around at some of those other brands.
I agree with the TJM winch report. I have the TJM, and it's failed twice within 2 years. The solenoid was covered under warranty, but the release gears have seized after 16 months. TJM then claimed the winch only had a 12 month warranty. And then they said any corrosion would be due to water ingress, and therefore not covered by warranty.
So I have two options. Get the existing winch serviced, or just replace the winch with say a Runva.