Okay guys, here is the "scoop" on the mufflers/exhausts.
Per Steve McPherson, Hatteras did not make these mufflers. These mid-80's vintage Hatteras mufflers were made by "Lyle Fiberglass" in Texas. Lyle was in business until several years ago. Mr. Lyle died and his son could not handle the business and subsequently closed it. Unfortunately, there is no one else who now makes them.
As "doc g" observed, the system is comprised of a muffler and silencer. The photos I posted show the silencers. The silencer is smaller than muffler and the "stuff" that is coming-out of the baffling is a material similar to steel wool (just as it looks). The baffling material is made to obsorb water which actually accumulates in the silencer as part of the muffling process. As I understood Steve, these mufflers and silencers came in three models -- MP-10, MP 11 or MP 11-10, and MP-31, depending upon whether the boat has 8" or 10" pipes. There should be a small sticker on the muffler and silencer indicating the model number(s).
The good news is that unless the silencers are leaking, and so long as the engine noise is tolerable, they are okay!
Steve advised that if (or when) they needed to be replaced, Sentek Industries, Inc., in Thomasville, GA (800.950.7653), would be the place to contact to have them make new ones. I think, rather than pay Sentek's engineers to design replacements from scratch, I would have MES retrofit the system.
Paul