I got bug spray on the face of my cell phone once and it burned into the plastic. Of course, I imagine a lot depends on how strong the spray is and what quality the plastic of the unit it also. You never know it, might work.
But be VERY careful putting any kind of cleaners on the screen of you finder. I found out the hard way that they do not hold up to the ingredients in Windex and it actually will cause the screen to "spider web" crack over time and become very hard to read. Plus, once that happens, the unit loses all it's waterproof ability. But I have never owned a unit other than my old Garmin that did not fog up in the sun. That goes for 'birds, and Lowrance both.