I recently replaced the stock exhaust on my 2021 Ducati Monster for a full system termi but am stuck with the old one now. It was always why I avoided mods - what to do with the old parts. What is the market for a nearly new stock exhaust for a 2021 Monster - some guy who crashed his? But what are the odds of finding a customer like that? So you are facing the same situation but in your case your chances are better as I am guessing a lot of those BMW bikes get damaged at tracks and even on the roads.