When I bought my 190e, the ashtray would push closed but not stay there. I removed the 2 phillips (or posi-driv) screws under the tray and unplugged the lighter wire. An examination revealed a small plastic geared lever on one side, which flips back and forth every time the ashtray is opened/closed. It had come out of its 'track' No tools needed to reposition it and it's been working fine since.

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1993 MB190e 104k