First of all, thanks to both of you for the inputs.
Second, Yes, I am talking about the front seats.
Third, your replies don't say, but I assume the repair can be done with the seats in the car, is that correct? The manual says to remove the seats to do a similar repair on the seats with manual crank-up headrests, and has no procedure specific to the motorized seats.
And when you say it is difficult to remove the back, do you have any suggestions or tips? It looks as if there are two screws, and then you have to release the seat back from the sides or edges, apparently by either spreading the sides or by somehow curivng the back, or some combination.
By the way, is this something not smart to do if you have a bad back?
Oh, and the $16 part -- is that one for each seat, or one for each of the two headrest posts?
Also, a friend of mine did this repair on a late-80s 560SEC and told me that he was able to repair the broken plastic piece with small hose clamps, which has worked now for several years. That sounds like what one of you is saying.
Thanks again.

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DavidB29
1992 300E with ASR
35 years of Diesels until now!