Offshoreonly.com - Exhaust Resonators

I have twin Merc 502 MPI's with one season on new Revolution Marine BB exhaust. Pulled the risers off to check things out and I see I am still getting small amounts of salt water into all the center cylinders (that is why I bought new exhaust). I am pretty certain there are not any problems with the engines. I know that Mercruiser used to recommend using the plastic exhaust resonators in the pipes of 454's and 502's, and I do alot of idling to get out of our canal. Are these things still used and do they work? I see they are still available.