That's true. And in most cases it's probably fine. But I did find it worthwhile to drill the rivets and take my ten year old silencer completely apart. Some smaller fibers had worked free from the packing over a decade of brappage and spooged themselves around in the spark arrestor, etc.
I seem to recall thinking I had done a good thing by opening up the whole unit. YMMV
This image is after cleaning. Those little holes on the spark arrestor were fairly plugged.
Or, it's more like they were covered over. Imagine fiberglass where spooge is the bonding resin.
Soaking in a parts cleaner might have done the job, but I don't have that available.