There is one other place they can leak and it's not pretty. Aside from the boot and oil seals, the diff housing can be broken from careless workers. In this case, the right side axle can be dropped if you don't have a jack under it while changing the right shock. This will result in a leak that will appear as though it's coming from the large side of the boot. Replacing this part or the clamps will not fix this and it will be hard to see unless you pull the boot back out of the way and have a good look.
In the one case where I saw this, it had a nice bit sized ( big mouth in this case ) chunk broken out that was all in one piece. I believe the center section of the rear axle is cast or maybe ductile iron and it can be welded back into place. However, the axle will need to be removed and taken apart to do the repair. The left side axle tube would have to come off and the crown gear removed. In short it's a big job for such a small repair.
Not likely your problem but worth checking none the less. I think Joe has posted about this and may be able to add his thoughts.