It's pretty easy. I think it is much better to reboot good German axles than replace with cheapies. Lots of good YouTube videos. I used redline CV grease - it's a red moly product with a very high pressure and temperature performance: (data from redline)

Lubricant 4-Ball Wear Load/WearIndex
(ASTM D-4172B) (ASTM D-2783)
Red Line CV-2 0.46 71.1
Syn Grease - M 0.50 41.9
Syn Moly Grease - A 0.78 38.4
GM Wheel Bearing Grease 0.71 36.6

Lubricant 4-Ball Weld Drop Point
(ASTM D-2783)
Red Line CV-2 400 Kg 900°F+
Syn Grease - M 2 200 Kg 485°F
Syn Moly Grease - A 315 Kg 515°F
GM Wheel Bearing Grease 250 Kg 525°F

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