I was cleaning out the airbox on my 77 CB550K and noticed that the element under the filter was basically soot. Totally disintegrated. This part has long been discontinued, there's even a thread on here from 2011 mentioning that someone tried using Uni Foam Filter but that it may have been somewhat coarser than they original element. There seems to be no aftermarket version of this part.
Has anyone successfully fabbed up something? I'm trying to keep things as stock as I can.