Yes it will, no paint = rust. Use a plastic putty knife or a brush.

That's true, but it doesn't take long for stones, sand, and other abrasives to do the dirty work.

plastic putty knife ..by far

Plastic will work for the grass that is easy to remove. There are also rounded, flexible metal ones that work quite well and are easy on the deck. I have those plus 2 heavy duty scrapers to get off the grass on the tough ones. I see lots of de-lamination underside of mowers that the grass has sat on- in fact paint comes off in sheets w/ the grass.

There's really no point in being concerned about paint loss under the housing. Just make sure its clean before storage and sprayed with some kind of preservative.

But you don't want to gouge it either. I use wood carpenter's shims to scrape the build-up off.

I have never routinely cleaned decks and in 50 years of mowing never had a deck rust problem. Most deck rust through problems are caused by decks that get a build up of dirt and debris on top that never gets cleaned off. Left outside to get wet in the rain they eventually begin to rust. The underside of decks gets blasted when the mower is used and almost never has a rust problem.

I agree. In the Fall, after mowing over sticks, hickory nuts, and dried up leaves, the deck is pretty much sandblasted.