E38 Electric headrest problem

Hi The electric headrest in my 740 seems to have developed a problem.

It will move up electrically, but will not lower electrically. If I push it down, it will move down to where it should be. The motor seems to be spinning on both downward and upward directions, and the headrest (if pushed) will lower to where 'it should be' (if it was being pulled down)..... ie. it will stop half way down, or go all the way down, if I hold the button long enough, and push...

I think there must be some mechanism that holds the bottom of the headrest, that pulls it back down..... There may be something wrong with that part, as everything else seems ok

Any help appreciated

Thanks