Morning Bill
Can't say if it hurts or not, but I've been doing it annually as a matter of routine maintenance for several years now and haven't sprung any leaks or blown the engine up or killed the heat exchanger. What I do is mix up a solution of flush in a two gallon bucket, close the through hull and pour it into the raw water strainer pumping it through the system and then shut the engine down. I let it soak for a couple of hours then crank it up and let it flush with lake water. I've seen small chunks of of what appears to be algae and other gunk come out of the exhaust and the exhaust water is almost always murky at first then clears up. This works for me in fresh water, don't know what it would for salt water. I would think that if your system is right on the verge of springing a leak somewhere anyway that flushing could go ahead and finish it off, but just guessing here. Luck!
