The rear of the cat pipe has two different seals. 126-997-00-41 is the graphite "flat cylinder" seal. This one is almost always reusable. I've never had to replace one. The other one is 202-492-02-81, the same as used for the front crossover pipe. This one is often reusable as well, but can be damaged if you pry against it while trying to separate the cat pipe from the middle/rear pipe.
The 400E comes with a one-piece rear assembly where the resonator (middle muffler) and rear muffler are welded together. The replacement rear muffler is a slip-fit, not flanged... you cut the pipe, and slip the new muffler over the old pipe, and clamp it together. Completely different setup than the flanged muffler/resonator on the 500E.
