I have never heard that. In fact, I just took my winch to Warn in Clackamas, Oregon and had it serviced 2 weeks ago. I have 9.5ti on a multi mount and they never once told me that. The only thing they said was, "you should bring it in more often if you submerge it or the gears will rust. One more year and you'd have had to buy a new winch." oops.
I always have it on the front of the rig on my long trips and haven't lost it yet.
The welds will break? Doubtful, but not impossible. Who did you talk to?