The doors on these machines usually fail due to a combination of factors which are due to ageing.
1. The primary rubber drive belts harden and stretch and should be replaced. Easy job to do once you know how to lift the lid.
2. There is normally a dust and sticky household grease build up in the sliding tracks at the top and bottom of the doors. Should be cleaned out for their full length with a cotton bud damped in iso propyl alcohol. Again an easy job, requires removal of the glass panels and the centre aluminium panel.
3. The drive strings become worn and fluffy and snag as they run around the spindles. Not an easy job and should be avoided where possible!
Instructions on how to dismantle the unit are in the service manual which is identical to the Beocentre 9500 manual on this site.