If the tarnish (it’s not rust), on the back side of the dial has you concerned, I don’t think you have much to worry about. The dial faces up quite nicely. You said, ”should this (I assume you mean rust) be a concern in a manual movement?” The only timepiece that shouldn’t be bothered by water is a sundial! Rust in a watch of any description should be avoided!
If the tarnish (it’s not rust), on the back side of the dial has you concerned, I don’t think you have much to worry about. The dial faces up quite nicely. You said, ”should this (I assume you mean rust) be a concern in a manual movement?” The only timepiece that shouldn’t be bothered by water is a sundial! Rust in a watch of any description should be avoided!
