I think there should be a release for the cushion.

My car - no power seats, has a little red tab just barely sticking out of the center of the bottom of the seat cusion per side.

Perhaps you have something similar on yours. But with the power rear seats it may be different.

Alon

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'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon - Sold
2006 E350 Wagon - 368 - Dead
2015 GL350 Bluetec - 197U