according to http://www.spares2go.co.uk/browse/PANASONIC/SD-BT55P/BREADMAKER_SHAFT_UNIT/m153/p3216/s6212.htm, that part is no longer available. Do you know whether it is leaking through the shaft mounting, or around it? If it's just around it, you may be able to remove the shaft unit and then replace the seal between it and the pan.
Nick, March 2008