Hey Mitch, here's some help from the factory:
"
The best thing is just a good washing with a mild detergent and water mixture. Do not submerse the unit in water and if there is gunk in the crevices a soft bristled tooth brush works great. " GREG HUNTER | c.s. TECHNICAL OPERATIONS SUPERVISOR | NAVICO AMERICA
And, this from the Product Manual:
Cleaning the display unitThe supplied cleaning cloth should be used to clean the screen,
where possible.
Where marks on the screen can’t be removed by the cloth alone, use
a 50/50 mixture of warm water and isopropyl alcohol to clean the
screen. Avoid any contact with solvents (acetone, mineral turpentine etc.), Ammonia-based or vinegar-based cleaning products as they may damage the anti-glare layer, plastics bezel, or rubber keys.
To prevent UV damage to the plastic bezel and rubber keys, it is
recommended that the sun cover be fitted when the unit is not in
use for an extended period.
Checking the keysMake sure that no keys are stuck in the down position. If one is
stuck, wiggle the key to free it back to normal.
Checking the connectorsThe connectors should be checked by visual inspection only.
Push the connector plugs into the connector, if the connector plugs
are equipped with a lock; ensure that this is in the correct position.
Hope that helps!