[No_Regerts]

Update: My wife's 2015 X5 50i XDRIVE with 105K mileage, starting doing the hesitation/slippage thing that many have reported, especially noticeable when accelerating up the hill leading to our driveway, or when noodling around town under 45mph. Anyway took it to our local BMW shop (not the dealership) that we have been using for normal maintenance on both our vehicles (mine is a 2013 328i XDRIVE) to diagnose. They confirmed it was an issue with the transfer case and quoted $6500 for a new transfer case and $3600 for a used one with a 1 year warranty. Needless to say, we were shocked and disheartened. I started googling and found this page (and another page on YouTube where the guy actually performs the procedure) and saw that many reported that it fixed the problem. So, not being very mechanically inclined, I called a different Euro shop and asked for a quote on a transfer case fluid change. $700.00!!!! So I watched the YouTube procedure a few more times and decided that it would be worth a shot to DIY. Keep in mind I am NOT a mechanic, and I'm probably the least dexterous person you'd ever meet.

Here's all the things I used/needed:
Foxwell NT530 scanner - $180 directly from their website
Redline 50604 70/75W GL-4 transfer case fluid - $23 1QT is more than enough - Amazon
Grip Clip Transfer Pump w1156 - $12 on Amazon
Lubrimatic 55-001 4CC Fluid Pump for quart sized bottles $9 on Amazon
CTA Tools 1136 Transmission Fill Plug Socket, 14mm Stubby - $12 on Amazon
I did not use the ratcheting type wrench as pictured in a previous post but I WILL BUY AND USE ONE IN THE FUTURE. HIGHLY RECOMMENDED. I just used a regular 19" closed end wrench with the CTA Stubby and it was more of a hassle than it should have been due to the lack of space.
New drain plug. about $10 from Rock Auto. I used it since I bought it, but I feel it's unnecessary. The old one looked fine (identical to the new one).

Also, recommend a drain pan (a clean one so that you can measure how much fluid extracted)
A Shop light for obvious reasons
At least one 3-ton hydraulic jack (two would be better, one for the front and one for the back)
4 3-ton jack stands
Shop rags to wipe down the fluid from the area (it's a messy job)

Procedure:
Jack up the front and back using the jack, place jack stands under and release jack so car is resting on jack stands. Make sure you know where to place the jacks while jacking and where to place the jack stands. I would try to get two jacks and do both a little at a time if you can. Make sure it's pretty level when resting on jack stands.

Crawl under locate and remove the old drain plug using the CTA stubby and your wrench. I had to use my foot to break it, since it was so tight. Some fluid will come out so place the drain pan to catch it.

Using the Grip Clip transfer pump, bend the tubing into a hook shape and force it in to the drain plug hole. Make sure you get about 4" or so into the transfer case. Then extract the fluid out. I used a clean glass Cafe Bustelo instant coffee container so I could see how much I took out. Appropriately, it was a dark coffee color and smelled nasty, like you'd expect. I was able to extract approximately 600ml. I probably could have got a bit more but it started to not be worth the effort.

Then, using the Lubrimatic 55-001 4CC fluid pump placed directly into the opened bottle of Redline transfer case fluid, I inserted the tube of the pump in the transfer case and slowly started pumping fluid in, until it started leaking out.

This was the hardest part. I grabbed the new drain plug and tried to get it started in the hole by hand. Due to the lack of space this was very tricky. It wasn't until I found the best position, with palm facing towards the front of the vehicle that I was able to use my oil-soaked fingers to slowly turn the new drain plug and get it started. Yes, the new fluid was dripping out onto my hand and arm while this was happening.

Then, and this is where the ratcheting-style wrench would have been a savior (lesson learned, I will buy one for next time), I slowly inserted the CTA stubby into the new drain plug and millimeter by millimeter, was able to tighten it up. Then I gave it a good tight turn at the end and wiped everything down so I could spot any leaks. None.

I was feeling pretty joyous at this point. The hard part was done. So I hooked up the Foxwell scanner and performed the transfer case recalibration. I had rehearsed the steps previously on my car just so I knew what to do. Leave the car off, plug the scanner in, let it identify the VIN automatically, then under BMW--> Service--> Drive Train you will see the function to recalibrate. Just step through that with the F3, F2 buttons following the prompts and it will complete in a few minutes.

I fired up the willing engine, responding with a roar. My wife hopped in and rode shotgun as we backed the car out of the garage slowly, driving it gingerly for the first couple miles. During this test drive, we looked at each other several times, not knowing what to expect. It is 10 year-old BMW after all. Then we stopped at the local gas station and filled it up then I let the wifey drive it home. It's her car and she knows it better than I do. We still were uncertain at this point, but as we approached the road that swerves up the hill to our driveway, the beast was perfect. The hesitation was gone. I FIXED IT IN UNDER AN HOUR and with less than $300 worth of parts/tools/supplies! OMG WHAT A GREAT DAY!!!!

Thanks to everyone on this thread!