The back panels of the W201 190 and the W124 300E are not equal! The back panel of the W201 seat is screwed in at the bottom and will fall down anytime these 2 screws are removed.
The W124 back panel is tucked in at the sides...I don't recall what is tucked in were exactly, but I think the sides of the seat are tucked in the edges of the back panel...and you need to peel that out. There are only 2 screws in the bottom of the panel; that is correct.

greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)