Here's the procedure for checking your fluid and for changing it. If you do change it yourself, the newer models do not have a drain plug in the torque converter. You'll only be able to get about 4 quarts out of the tranny with a filter change if you can't drain the converter. If you have an older model and can drain it, you will get about 8 quarts out of it. I hope that you can read these screen shots.
I changed mine at 42,000 miles. It was dark compared to the new Mercedes fluid. It needed changing.
You can get what you need at the websites others referenced. I went to thepartsbin.com to get my Mercedes fluid and parts.
My rear differential fluid looked really dark. It needed changing. I used Mobil 1 75w90 gear oil from a local parts store.
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