The seals / gaskets mentioned above are correct, however they are re-usable unless damaged. Separating the twin pipes at the back of the catalyst can be extremely difficult. The bolts may break, the link below shows part numbers for the photos. Note the 500E has a bolt-on rear muffler, the 400E does not.
Photos are at this link:
http://www.w124performance.com/images/M119/exhaust/
