mnwolftrack's post is exelant.
I've found that the rubber boot causes more harm than good - at least in a truck that gets used in mud and deep water - it seems to hold in more than it keeps out. Once the lever is free, and the boot is cut off, it is easier to keep it clean and lubed. After being in mud give it a good blast with the pressure washer. Whenever you have a lubricant nearby give it a little dab or spray.