They are vacuum actuated. Check under the front of the seat and there will be
a vacuum line. There will only be vacuum with the car on and the doors closed. The button on the seat just bleeds the vacuum off.

Aha! that was very helpful, I'll look this weekend if not sooner. Many thanks

Yep - It was a lose line. Now it works fine. Many thanks!

strangely enough when i picked up my 300ce the vacuum line was disconnected as well, is there some rationale behind this or does it come loose over time?