Great news that you solved the speaker problem – many people have left a headphone adaptor in the socket in the past (it is neatly hidden), so live and learn!
With regard to the door, I think the motors are supposed to run for a fixed time, rather than stopping because of a sensor. However, the motor probably will stop if it senses resistance.
Maybe have a look at the following thread for some suggestions about cleaning and belts, but if you are going to take the BeoCenter apart then the service manual will be a great help – you need to be very careful with the top and bottom glass panels when putting the unit in the service position, because they can drop out if the glue has perished.