Dick, the rear sight is in near perfect condition, threaded holes are un-messed-with.  I'll check for burrs, crud, etc. but I removed the rear sight, put the screws back in the holes, and found the screws were also off center by .015".  So, it's the threaded holes themselves, not the rear sight. 

But you know, I'm not sure what to use for a reference surface to see if the rear sight is off.  I was using the rear underside of the magazine box as a horizontal reference.  Maybe I should use the extractor notch in the receiver to find the centerline?

I'll try to post a couple pictures soon.

In any case, when I get the new front sight I'll align it with the rear sight.