I have it mounted upside down, and it's worked fine for years. After a recent week of daily riding in heavy rain, water entered (my fault, of course) and there now is brown corrosion visible through and on the front lens. It still works, and I'm tempted to leave it alone, but I also wonder if I should attempt to remove the front housing (apparently it simply unscrews) and try cleaning it out with contact cleaner or somesuch. (The argument against it is that I haven't the slightest idea what I'm doing and could easily mess something up through ignorance.)

Thoughts?