The mechantronic sealing sleeve is locatated just above the pan on the right side of the tranny. It protect some plugin. Older ones are known to leak (mine left a small puddle after seating for 3-4 days).
Stupid thing is the locking mechanism to hold it in place is IN the oil pan so you have to do it all.
The part is cheap- $10. Plus the pan gasket and oil.
Not required in a tranny oil change but if you have a leak it may be the culprit.