Well, I'm pretty sure you can wash in the winter, I think just not right after the Krown treatment. It's supposed to penetrate into the tight spots and cracks and prevents salt water from sitting in those cracks. Surface rust is something that's preventable by washing but when it comes to areas of stagnant water, it's pretty hard to wash out (and that's where rust forms usually). It's like when you put skate guards on your blades after a game and you don't wipe the blades off first (or they don't dry completely), you'll get a lot of rust quickly but if you let them air dry before putting them away, you won't get that rust.
And I was told that not all 335's come with oil coolers? Could be the older models? At least I know I have one on my car (had Budds look it up using my VIN).