Go to Wal Mart or an automotive parts store, look for a biodegradable cleaner. Castrol has one, and then a supply of painters rags, rubber gloves and see if it helps. I have a similar product, it desolves gas, oil, on engines, parts and concrete. I usually use a light mix of Dawn and warm water afterwards. Any remaining order might come off with Moth Balls, or Baking Soda. Put the items in a box with the above, seal and wait. Remove the batteries from the GPS first.
opt. 2. call the manufacturer,
opt. 3. search online for a solution