All of the searches I've done seem to deal with the opposite of my problem. My rear headrests will not stay up. When I press the dash releaseI can hear a slight vacuum noise, but the headrests will not stay up. Any help much appreciated.

Thanks

Hmm, are you giving them a good tug towards the front of the car when you put them up?

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1981 300TD
2005 C55
2004 E500
1999 ML430
1992 400E
1998 C43
2001 SL500
1988 300SEL
1986 190E 16V
1991 190E 2.6

I believe so but will give that a try. I've tried both and neither will stay up. I also have a 300ce and they work fine.