If the navi is working, whatever cleaning procedure is applied will likely cause the intermittent connections to go open circuit. In other words the navi may not power up again. You will be left with that sinking feeling which comes when a very valuable item is destroyed accidentally. So plan what to do if this happens and don't panic.

Avoid contact cleaners!

But in case you really want to clean these oxides away....use a glass fibre based "pencil" type cleaner available from all good electronics shops. Use it very lightly on the components, clean away residues with a cotton bud dipped in acetone or isopropanol.