Good for you for staying away from blocks <img src="/forums/images/graemlins/kewl.gif" alt="" /> ....blocks lead to axle wrap and take-off shutter.

re-arching the leafs might sound like the fix....but that damn memory they have will result in them sagging back down. The combo of re-arching and an add-a-leaf will slow down the sag process. A combo of re-arching and re-heat treating and add-a leaf will last longer. Each time a leaf is re-heated it looses some of its carbon content....and becomes weaker also.
Basically, I've been dealing with leaf issues since about 1985.....some people have great luck with the packs and some are stuck in hell. A simple thing like a long shackle that is kicked back too far could stress a leaf pack and cause sag. I like my dual coil assist solution personally. (bottom left of my homepage)