The inners boots do not go as often as they do not hae to flex as far as the outers as they have to follow the front (steering) wheels. It's the constant flexing that does them in. I remember reading about early failures on the Explorer site when people put lift kits in. Again the boots have more flexing to do because of the kit and it really chews them up.

I called the dealer services and they told me that they replace the whole half shaft, which means replacing the whole thing. But after called talk to service manager and he told me may be just the boot itself unless there is a problem with a cv joint start having some noise. There is advantage and disadvantage of replace partial or entire half shalf, cost more for the whole thing, waist more times if it's only replace partial. If the dealer replace just the boot I would rather replace them myself, but my car still under warranty I will spend $100.00 for deductible each times it get fix.

Just a thought on premature CV boot failure; it could be that the early failures occur on vehicles which the driver tends to park with the steering in a turned position thereby putting the boot in a constant streatched/stressed position for many hours/days until it finally yields.

I personally ALWAYS leave the vehicle steering straight when parked to preclude this potential stress. I currently have over 82,000 miles on my 2001 4.4i without failure.

You cant do that in San Francisco, you will get a ticket if your parked on a hill and dont curb your wheels, and if someone bumps you and you roll into the car in front of you because your wheels are not curbed, you will be required to pay for the damage to the car you hit.

I always park straight, garaged at night, etc. These boots never had it so good!! :-)

Regarding replacing both sides at once, my independent mechanic did do both sides at once, and my extended warranty covered it. But replacing halfshafts etc. was not necessary after he inspected them. I think we caught this pretty early after it cracked.