The boot kit can be had for about 25-30 bucks and has a Volvo list of about $95.00. There are two schools of thought on this situation, 1) Reboot boots that are cracking but have yet to split open and if it has actually split open and allowed crap into it then replace the axle with a rebuilt unit or 2) Just reboot the axle regardless of whether it has split open or not and just do a good job of cleaning up the innards of the ones that have torn open and allowed crud to get into them. Myself I have always subscribed to option #1. If you know what you are doing and have the correct tools then rebooting it is not that big of a hassle but the first couple you do might be a bit of a nightmare unless you have some real good directions and the correct tools. There is a fair amount of technique that goes into this job. On the other hand a straight forward axle replacement is just that, straight forward. Take it apart, replace the axle with a reconditioned unit and put it back together.

Mark