The M5 came with an aftermarket Billy Boat exhaust. It looked nice, but I found it to be very loud. Because I didn’t put it on, I didn’t have any experience to compare it to the stock exhaust. I took it to a muffler shop and they assured me there were no leaks. After a while, I learned that I had to coast into my driveway with the engine off to avoid disturbing my neighbors at night. This was not sustainable.
The decision to go back to the stock exhaust was the first of many to return the M5 to as original as possible (and avoid the slippery slope of euro mods or other “improvements”). It took me a while to source one, as new units or NOS by then were not available. Eventually, one turned up on mye28.com and after figuring out how to get it delivered with reasonable shipping costs, it arrived and I had the B&B swapped out. It was sold later to another board member.