I have no reason to say that the SDM is fixed or not, except that the forum chatter about failures seems to have gotten less over time. That maybe is because of a fix, maybe it is because they are just selling fewer of these lenses, or maybe more folks are just converting them to screw drive.
As to the lens itself, it is a nice lens. Biggest faults are weakness at the very wide end (gets better stopped down) and tendency to flare (I think most zooms in this range zoom a fair amount compared to primes). Still, I have used it a lot over the last four or five years and it has been quite dependable and given my a lot of photos that I treasure.