I have yet to see it but inside the stock 996/748 can is a stainless steel unit with a baffle (ever try to drill it out? I did). BCM will send a perforated core piece and a couple of weld on sockets for it. You remove the end cap and then the shell and packing. Install the new perferated core, packing and shell and re-rivet the end cap.
Note: this is what I have been told, I have yet to do it. I should know a lot more next week!
Mike