If you are not sure how to check Hendrickson pivot bushings on air ride trailers here is a pretty basic way.  (but not the only way)

1) Release brakes on the trailer
2) Make sure air bags for air ride is inflated
3) Simply push on the top of the wheel (or torque wheel nuts with torque wrench)
and if it wobbles the bushing in gone and i provided a picture of a worn out bushing