Getting rid of slight spur wobble

[simplechamp]

So I've been using my 52T Slipperential in my truggy for awhile now and I absolutely love it. Best upgrade I've ever bought, by far. Only thing is right after building it there was a slight, very slight, wobble in the spur. I tried a few things to remedy it (retighten cap screws, reseat slipper pads, reseat teflon bushing, change orientation of spring washers) but I couldn't get rid of it. I figured maybe it just needed to be run in and would go away on it's own, but so far it hasn't. It's not a big deal because it's very small, the spur and pinion aren't wearing awkwardly, so I wrote it off.

But then tonight I built my second one, a 46T for my buggy, and the same thing happened, slight wobble. This time the slipper pads needed some sanding to fit, but I did that, and also tried all the other things, but there is still a slight wobble.

At this point I am thinking I must be doing something wrong, but I can't figure it out. I follow the directions to the letter, make sure everything is seated perfectly, make sure all the screws are tightened uniformly and in correct order. As I already said it's not that they are causing a problem, it just kind of nags at me because I know they shouldn't do that.

Anyone have any ideas? What am I overlooking here?