I've done this on every Benz I've ever owned, including my old 300CD. I usually replace it end to end, to avoid messing with rusty flanges and slip collars. Flanges aren't all that hard to deal with...if the bolts don't turn, you can usually just grind off the bolts. If you're trying to seal old to new, I have a product that will help you quite a bit: CoolCat Express Corp.: Walker Acoustiseal Exhaust Sealant I have to agree that the best way to do this is to drop the entire mess as a unit, and then replace with new. It ends up cheaper in the long run, and it works right the first time.