I don't know of a way to inspect the front drive shaft splines without removing it. The good news is that a stock front drive shaft will come out without removing the front diff or transfer case. Unbolt the front guibo and then slide the driveshaft forward until the splines are free. You may not need to even take it all the way out - once you can see most of the spline, you should be able to tell if they are worn/messed up or not.

Make sure you have the wheels chocked before you disconnect the drive shaft!

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David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles