[Spridgets] Tapered roller bearings

[derf]

First, try switching the nuts.  You may find one works better on the other side.
Then, I wouldn't fool around with shims.  Just set it a little loose
or tight and go with it.  I would lean toward the tight side.  As long
as it turns freely and has no end play, it should be good.
Third option is to replace the bearings and see what kind of
adjustment you come up with.
Have you inspected everything?  One notch from binding to too much end
play seems too drastic to me.  Are you sure the 12-6 rocking play you
are feeling is the spindle bearings?  More likely the A-arm bushings
or lower pin are getting worn.
Cheers,
Derf