I changed my Xdrive fluid for the second time at 180k miles tonight. I had planned to do it every 50k or so but never found the time. I was surprised to see the fluid in better shape this time after the same 90k interval. Still dirty but only about 60% as black as the first change at 90k. I did not reset the adaptation values the first time and had no trouble so I didn't bother with it this time either.