I just removed mine yesterday. Pull UP on the handles, and then pull UP on the cushion. Don't pull forward on the cushion until it is dislodged (you have to pull up to do this). If yours is really that difficult to remove then I am guessing somebody may have really jammed it in there. The seat is supposed to be very easy to remove because your battery is located under there. Seriously, something doesn't sound right.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280