It's never a bad thing to buy new things, I do that myself all the time
Just sometimes you don't have to go that way. Water in the engine won't neccesarily cause your oil to go milkshake. Not at once, only over a longer period. I only noticed after a thousand miles or so of using my "new" engine. And as I said, it's only a thought, and it's never a bad idea to do a comp test, just to be on the safe side. But of course it's your free choice
Best of luck,
Max