I've typically seen longer than 100K service life of the brush pack/regulator assembly.

For me its been more like 150-200K. When you replace the brush pack take a good look at the armature, if it has a noticeable grooves and the surface appears to be rough its almost mandatory to clean up the armature in a lathe.

If you don't do this I've found the new brush pack will be worn out in 30-50K miles since the new brushes will be pushed into the armature with more force than the old assembly (new springs and more compressed in the new brush assembly) and they subsequently wear out rapidly.

If the armature is cleaned-up you can expect another 150-200K but at that point the bearings are usually a bit gritty to say the least.

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98 Dodge-Cummins pickup (137K)
13 GLK250 (157k)
06 E320CDI (341K)
16 C300 (89K)
82 300GD Gelaendewagen (54K)