the panhards are not far enough out to be the sole cause. (20-25mm) is significant but not the only factor. springs do sag over time especially if they are working close to their yeild point (the case with all performance well matched articulating suspension systems). springs like these are a disposable comoditity. racing etc you are lucky to get 12mths, so a few years of normal use and they are shot.
when you set up the springs you generally put the longer coils in the drivers side. so the shorter ones end up on the passenger side which is the direction of the lean described above. as the springs yeilds the weight balance on a truck with a high c of g begins to put more weight on the lower side compounding the problem.
as the springs are then forced regulary past the yeild point
the more the sag etc etc...
if you don't want sagging springs you need to go to a harder a rate spring which limits articulation hence defeating most of the point of a lifted truck.
man up and replace them if ya want a big truck that works. they are 195 - 250 a pair depending, which is a lot cheaper than the embarrasment of a leaning tower of landcrusier
cheers mate bru