Rigid R2600 ROS problem

I have 2 RIGID R2600 5" ROS. I just noticed yesterday that my sanding disks only wore the outside edges, after putting a straight edge to the pads there is almost a 1/8" dip in the center. Is this normal? Does this make a difference? I looked at a Bosch and a Makita and both were flat.
Why 2? 1 broke after a little over a years use and I had to mail it to a service center so I bought another one since they were offering a lifetime warrenty.
I'm going to return the recent one and step up to the 6" RIGID R2610, they're made by Metabo and should be of higher quality.
What to do about the dished 2600 pad? Replace with an aftermarket more contour pad?
1 broke and I had to mail it off so I bought another.
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