I can neither confirm nor deny that back in the day we had terrible grounds on main seawater pump motor, ended up brewing up some some super-deionized reactor grade fresh water and flushing out all the windings. A hella’ lot more than 6 gallons. Dried it out meticulously. I’m not suggesting that this was on a submarine, or even that it actually happened. However, whether or not we did this …. It worked great. That motor lasted the rest of the patrol, no problems, good to go. Hypothetically speaking, of course.
So I agree, rain water not the worst thing you could pour on a Yukon.