Front seats won't lock upright in a w124 coupe
 

Have a 91 300CE. The vacuum door locks and trunk lid work fine.

But the front seats lock-in-place mechanism does not work. so a hard stop has the passenger seat diving forward. (I'm sure drivers seat too, but i'm IN that.)

Also the rear headrests (coupe) will not go down when the dash switch is pressed. They stay locked in the up position.

What's likely to be the culprit and is it a straighforward fix? Thanks