My first boat was a Zodiac with a 50 HP Johnson, 1970's era. Bought it used from a dealer. When I did the test run, as he was setting it up, he grumbled it (boat & motor) had been on a trip to Baja and was wondering if the guys using it had flushed it out.
Yeah, right! Shortly after taking possession I noticed poor flow through the tell-tale. Poked a wire in and hit something. Pulled the water jacket and found it was packed with salt and half eaten through with corrosion. This presumably from a 1 week Baja trip (although now I wonder if it had ever been flushed).
I should have taken it back and demanded either repair or new motor. However, I just got a new water jacket, fixed it and moved on.
Anyways, now, 40 years later, it is flush, flush, flush. I also run some SaltAway through frequently.