I rebuilt the armrest on my 92 400E 1.5 years ago, here is the thread:

http://www.peachparts.com/shopforum/showthread.php?threadid=29222&highlight=rebuild+armrest

The cost was $7, it has been working great since then, just be sure to reinforce the plastic frame with something (nylon cable tie etc..) after glue it with two part epoxy glue.

The armrest is weak, it was not designed for supporting body weight other than an arm.

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99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.