Flex metal electric conduit may fit. Factory exhaust and muffler is all one piece. But there's no reason you couldn't cut off the damaged flex section and install any appropriated piece of metal tubing. It is held on with a clamp around the heaters outlet tube.
My recollection is that there is one MB OEM fastener on the Eberspacher exhaust pipe. I removed that fastener one time and never re-installed it even with subsequent R&R repairs of the heater. Once in place the flex pipe stays up in position where it is needed. It isn't like there is any exhaust pressure to speak of. A snug flex pipe on the exhaust shouldn't need any clamps or fasteners.