From what I have seen all have it because there are no bearings on the slave side, just plastic bushings. I think it's a must do mod. You might not notice much till you compare it to ours with the mod. If your servos were noisy it could be you have a servo arm off by one spline and that it was under a small bind that coveres the slop.
When I called Traxxas about this the tech I talked to grabbed a new E-Maxx and it had same slop. He stated it was normal and not to worry. I just wanted it to track straight and be smoother so I fixed it.
By leaving out the one link it still smoothes everything out better then stock because you now have nice bearing to support the slave side. You could just get bearings for the slave side but they'll be real small.