I'm thinking you are talking about the LRE suspension on your rig. I replaced our rubber springs a couple years ago, thinking the rig leaning was caused by a failed rubber spring, but it turned out to be a broken leaf spring. As I had already replaced the rubber spring on one side when I discovered the broken leaf spring, I went ahead and replaced the other rubber spring. This is the link to the owners manual, which has information on how to inspect the rubber springs.
http://www.morryde.com/uploads/downl...%20Updated.pdf
This is a photo of the used spring and the new one next to it, so after a number of years, the used spring had deformed some, but it was actually still serviceable and not cracked which would have made it necessary to replace it.