if its just a matter of slight sag then rotating the inner/outer torsion splines should do the job it maybe that a PO cocked up a rear drop or ballsed up the splines by accident....
Had the camper for 6 years,just noticed it when getting it ready for summer ,so whats best to do,turn splines or new bushes? or when iam there i do both? its a lot of work doing bushes if i have to go back and do splines.