After moisture was in mine for several years, the hour/rpm faded slowly until you could not read it anymore.
Now, anytime I wash mine, I remove the dash before I start.
It's barely sealed at all, it just snaps together. If you spray water thru the screen into the battery area, moisture comes up from the battery area and condenses on the instrument 'glass'. There are a couple breathing holes what looks like a permeable fabric covering them.
I don't think you can prevent the moisture/condensation. And I don't think it will bother anything. It might make sense to wash the tractor hot and let it run a little to dry off the battery area.
I pried mine out with a screwdriver from the topside. There are no 'clips' holding the instrument cluster in, it just presses down into the dash bezel and is retained by friction. Maybe it can be pushed up from below (above the battery). I did not try this but it looks like you could remove the screen (by your knees) and stick your hand up there and push it out from the underside.