Stainless steel, actually.
The original silencer has had it. Its made of stainless steel as well but the innards seem to have rotted away. The sound it makes is just a harsh racket.

So, been looking for a while and in the end, a chance email conversation with Mat Beekers of bmwboxersupplies resulted in me buying a unit off their demo bike.

Its a slip-on end can from BSM in Germany.

Very lovely it is too. Makes a nice sound and that’s with the DB-Killer in it. Its got quite a large outlet of 55mm so it will probably be a little loud…

Oh how we love our toys!