When you remove the return trans fluid cooler line for a complete power drain you might be able to use the two ring seals.. BUT
To prevent potential fluid weeping on the end of this pipe fitting that attaches to the right side of the transmission, you might want to replace these o-rings if you end up removing the pipe during your 722.9 transmission service.
722.9 Transmission Oil Cooler Line to Transmission Housing Seals x 2
$6.40
SKU:
TRS-722.9COOLERSEALS 
Product Details
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722.9 Transmission Fluid Fill and Power Drain Service Kit
Pressure tank included. From 2003 to 2016, 7-speed automatics require filling from under the car. For use with Red or Blue Fluid. Video instructions included.
It comes with a special fitting attachment that includes two (2) shut-off valves ( to control spills) and a clear filter to make absolutely sure you are putting clean fluid into the pan. It includes over 5 feet of hose ( 30 inches which are clear so you can see the
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Early 722.9 Transmission Pan and Filter Upgrade Kit w/ Video Instructions
To increase fluid flow. The best thing you can do to increase the life of your 2003 to mid-2010 7-speed transmission.
Many enthusiasts are now buying these 2004 to mid-2010 high-performance Mercedes with little thought to the transmission.