Arthur, I checked out the 458B on the web catalog. According to that, it is water sealed only within 18 inches from the bottom of the leg (only at the joint between the lowest and the second sections).
....
Seemingly. And I dare say marked as such to help them avoid warranty claims.
I've had mine now for a good 12 years, been underwater many times with zero issues. No corrosion, no leaks, no water trapped.
One possible way to cause issues to any of the legs tho could be that if a leg was extended while the sliding joint was fully immersed. Can't say I remember if I've ever done that tho.
My primary setup technique: fully extended before entering water, and close to the required level whilst in there.
Leg construction itself is as solid as any. Couldn't estimate how much force is required to compress the leg without the use of it's close button, but it'd be immense.
Leg could bend if treated brutally tho, so care would be required there. I'd say that if such brutal treatment of a leg were to result in it bending even just a small amount, it'd be pretty much totalled tho.
But as I said earlier .. the top plate/leg junction area does feel a lot less solid that the likes of Gitzo/Benro type solid constructions.
It's a multi piece design, and I haven't yet figured out a way to dismantle it either. It is metal, but it feels plasticky .. and cheap.
But in saying that, it's survived the rigours of my car for over a decade!
That may not sound like a rigorous environment, but when 4WDing .. it's not as cushy as your normal car environment!