This 17-year-old article (Mercedes Benz w123 as “New Youngtimer”) simply describes exactly the presence of shut-off devices for exhaust cleaning as if it were the most natural of the world: http://www.wurmkat.de/presse/oldtimer/markt/abgastest/abgastest.htm Maybe one or the other finds interesting, shows how ridiculous the “We have all never known anything sst” from KBA etc. is…. Have fun reading the scrap metal fanatic wishes