Sea Ray

My guess is the boat has twin Mercruiser 5.7 Horizon engines w/ raw water cooled exhaust. Please identify / confirm the engines.

http://images0.boattrader.com/resize/1/11/4/6561104_0_290120181349_137.jpg?t=1268633

If the boat is operated in salt water, then the OEM Mercury parts are good for 3-5 years before they must be discarded. Aftermarket parts cost less and have a shorter service life.

The service life in fresh water will be longer.

The best option is to unbolt the elbows, clean off the gasket surface, then inspect for the SOLID wall thickness between the exhaust passage and the raw water passages.

The parts are discarded when the solid wall thickness has deteriorated to an insufficient thickness.

This inspection should be performed annually after the second year of the exhaust parts being put into service.

When required, replace the manifolds, risers and elbows together on both sides and both engines.

On my salt water 454 Horizon engines, I designed and installed a custom fresh water flush system to run fresh water, soapy water, then Salt Away after each use. Then I drain the parts bone dry, instead of the original design that had the bottom of my manifolds wet 24/7/365.