Guy is right all the way down the line.
Tim,
Stainless is subject to a nefarious deterioration due to stress corrosion cracking. Stainless relies on the presence of oxides (oxygen) to maintain it's corrosion resistant properties. There are environments like exhaust systems where that really doesn't work. There are other grades of stainless like Gr 410 that work pretty well in those exposures but not readily available to us.
Just a reminder, when reinstalling whatever you build do not forget to include a vaccuum breaker in that water injection loop. Pictured below is the way my new-to-me 3HM35F was set-up with that short jumper hose to the water injection nipple. Seller had that hose on there when he shipped me the engine and that's the way the engine and it's new ZF Hurth marine gear and drive saver went into the boat.
Day after launch I was aboard and went to start the engine, noa-goa. Checked battery voltages since I didn't have the charger hooked up yet. Flicked the de-compression levers and she spun over easy, then started the engine. Logic was she had cooled from the run after launch and ingested seawater. Took the jumper off and replaced it with hose feeds via the existing vented loop, well Duh!
Actually did this one other time with fresh water home in the yard. After haul-out and extended layups I like to periodically start the engine. I would usually stand a 5 gallon bucket in the Galley and place the raw water intake hose in that Pail. And a hose handy to top it up.
Got smart one time and figured I could just connect the garden hose directly to the raw water hose and eliminate the intermediate resevoir, not! By the time I was back aboard from turning on the hose, water was spewing out the wet exhaust obviously the pressure was by-passing the flappers in the impellor pump. Water in the engine again.
Again, spun her on de-compression and then started her right up and then warmed her up, no water in oil, all was good!
Hopefully I don't live so long that I have to start learning these "Lifes' Lessons" all over again. And if you can't laugh at yourself....... S*** I can't remember!