Front drive shaft boots
Our X3 has suffered through a number of front axle issues. Fortunately, all but the struts have been covered under warranty. We purchased the X3 as a CPO with 36k miles on it. Due to steering wheel shake under beaking, the dealer went through 2 sets of rotors and then elected change out the calipers on the 3rd pass. Problem solved. Then one of the front struts went at 65K miles, so we shelled out to have both replaced. Within a couple weeks of the new struts I did an off-cycle oil change and discovered lots of red grease splatter in the FL wheel well. I suspected a crack in the outer boot which was confirmed and fixed by the dealer under CPO extended warranty.
My point here is that since you don't need to jack up an X3 to change the oil, it makes sense to check out the front axle every couple of months to make sure everything is OK. I'm convinced that all of the front axle tear downs that went on with this X3 contributed to the boot failure and I was lucky enough to spot the problem before the front axle got destroyed. If the front axle got destroyed my basically free boot replacement might have morphed into a much more expensive wear-and-tear job where I would have had to foot the bill.
Since I'll be going out of CPO warranty in the spring, I know I'll be checking underneath once a month as part of PM. Sure you have to get down on the garage floor but it only takes a couple minutes - and might save you a fortune in the long run.