I am running an older 454 Mag with Stainless marine exhaust.
The rubber flaps on the tailpipes don't seal anymore....
Do I need to replace these?
Are there internal flaps to keep the water out when the boat is on the dock and not running?

call trick marine and get a new set... they are too cheap to mess around with not having them.

Would I be able to see the internal flaps if the were there?
I can look in the exhaust..... the left side has a small square edged piece that blocks about the bottom 1/8 of the hole. The right side looks deep dark and lonely. What is the square thing? I poked at it a bit..... It seems quite secure.
I don't think there are any flaps in there. I leave my boat in the water all summer. Should I get internal flaps as well as the rubber ones?

I have the 454 mags with stock diverters switchable and I have both the outer rubber fllaps and if I look inside, I have another set of flappers aft of the diverter switch. The internal ones have a top and bottom piece that are attached to a single hinge going through the center of the 4" pipe. I'm not familiar with what Stainless marine does, might want to give them a call. If you also have exhaust through the outdrive, there is another set of flappers down there which are located at the top on either side of the BIG U shaped exhaust. If you pulled the diverters off either side of the motor, right underneath you will see the flappers. These flappers, depending on how old your motor is have been changed to a new type as the old ones had a tendency to break and fall into the exhaust tubes..... Again, not sure if you have diverters or not and what year your setup is.... Good luck!

I am running thru hull only. I am just concerned water may get in the exhaust when it is on the dock.

These are the ones I'm looking at for replacements...

http://www.eddiemarine.com/cart/deta...CategoryID=139