In all the heavy use this lens has had, there has never been any problems with zoom bearing failures or dust in the barrell or other problems.
There has been a lot written about the push-pull design of the zoom. I do not find it a problem at all. In fact, I have gotten to like it much better than the twist type. When I have it mounted on my tripod and am zooming to frame (no I cannot use my feet to zoom or I would fall in the water with mud up to my knees or be in blackberry bushes ) the push-pull is much easier for me to use. No twisting involved. I do not find this a problem at all.
The other thing written about often is that the zoom is a bellows that sucks dust into the lens. Again, I do not find this to be the case. I've wondered where this idea comes from. When you think about it, push or twist, if you are moving the lens barrell and it is not an internal zoom, it will move. Why this is supposed to be a dust sucker in one case but not the other does not make sense to me.
This lens has been all over the Northwest, back to the east coast, on an Alaska Cruise at sea and I've had no problems with it.