here's the thing, BMW can charge you $1300, but how many M are going to buy OEM M exhaust. The exhaust is so specific to our cars, and the majority of M owners are buying aftermarket exhaust. Therefore, why pay 1300 for OEM when you can get Remus for ~1500. In conclusion, used OEM has no value aside for what it's worth as scrap metal.
Unless you wait a few years we most of us are due for smog. hahaah, then the price of stock exhaust might goes up. good luck with the sale.