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.