If you have air bags then you may have lost pressure in the left one. If not maybe you have only just started noticing slight differences in your rig. Have you ever weighed the corner weights to determine how heavy the left side is compared to the right?
I had a 32ft Class A once that leaned left due to big slides and such. I added one long extra leaf in the left spring pack and brought it back to an acceptable state. I doubt you need a complete spring pack. If indeed you do have a broken leaf, and it does happen, you would only need to replace the broken leaf.
