My spare wheel is on the right, so that should contribute to a right-sided lean, not left. The off center driveline, the fact that the differentials are on the right, and the right-sided transfer case all should make the lean go to the right, if weight were the issue. Unless, like Jonathan says, the engine and tranny completely neutralize them. These factors are there all of the time, unlike a lone left side driver, and I should think more than compensate for the driver on the whole. So, I am not convinced at all that it is a weight factor unless the Toyota engineers put the engine and tranny too far the the left. Virtually all of the '40s that lean, lean to the left in the rear (right or left side driver). I therefore believe there is something else intrinsic to the issue, but I don't know what it is. Adding a leaf and stiffening the suspension on the left is a solution that works, too. I don't know if it is only cosmetic like putting in a shim, but I'll bet it is more expensive. Shimming was the official Toyota "fix" for this problem, (Toyota Service Bulletin; Volume 5; Reference, Body; Number 10; November 14, 1976; Model FJ; Title, Body Slant), so that is what I have done.