Connecting sleeve for the original rear muffler or for the installation of 50.0718.00 / 50.0719.60 / 50.0719.73 / 50.0768.40 / 50.0770.60 / 50.0770.73 / 50.0816.40 / 50.0818.60 / 50.0818.73 on the original centre muffler