The  moving parts that endure wear in a tandem axle RV suspension are listed below:

•    Four leaf springs, fatigue unevenly over miles and time. When leaf springs fail, they tend to break where the shorter lower leaf meets the upper leaf.  Sagging leaf springs stress all parts of the RV suspension system including the tires.
•    Eight spring eyes, appear round, but are not.  The spring eyes are not a machined surface, they are just flat steel formed around a mandrel.  Bushings are used to lubricate the spring eyes connected to each hanger.  The spring eyes are high bushing wear point due to their irregular shape.
•    Four shackles, connect each inner spring eye to the equalizer.  Bushings are used to lubricate this roughly surfaced movement connection.  
•    Two equalizers, one on each side connect the springs through the shackles.  4 Bushings in these connections are a high  wear point due to frequent movement.

There are 14 bushings in a tandem axle suspension, 22 in a triple.  

Bushings are important components of an RV suspension system.

RV Ride Control Education - Moving Parts in A Tandem Axle RV Suspension