DO NOT put oil or grease between leaves on a leaf spring. It will attract and hold dirt and will act like sandpaper between the leaves. If you want to let them work better and smoother, take them apart and hit them with a flap wheel to clean them up. Replace the teflon slders on the tips of the leaves and for extra slipperyness you can paint the contact surfaces with a product called EZ-Slide(you can get it from Tractor Supply Company). Then reassemble the pack and spray the outside of the whole spring pack with Rustoleum Professional enamel. Slap in your new bushings and it will be like new.