Found code VTG "55C4 - No Message from DSC." There're no warning lights on the dash. Drained oil, there was plenty - it was dripping when I opened the fill plug but very dirty. Refilled with fresh DTF1 from the dealer ($45). Successfully performed Transfer Case Service procedure for oil change using ISTA software.

Will report back if the jerking and code disappear.

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'05 E53 X5 4.4i, '97 E39 528, '07 E92 335i, '16 F86 X6M.