The panels are available from your dealer but only in sets of three.
It is not possible to replace individual panels as the colour of the anodising will not match and the new one will be obvious from the other side of the road.
Once the Beocenter is opened upit will be easy to spot the fault which could be a rubber drive band or disconected strings. Either way, it should not be too expensive to repair if you can find somebody capable of doing the job.