Well, I ended up doing a Transfer Case service. It was pretty sludgy and ugly after 120k, and there was also a leaky transmission seal. Also replaced front bushings, as one was torn. Hopefully with having the valve stem seals done a couple years ago, and this, I'll get another 120k out of it. Under 2k for everything. Thanks all for the guidance.

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1978 E21 320i 1980-99
1985 E28 533i 1999-2001
2006 E53 X5 4.4i Build Date 6/06 2012-