I think this should probably be in the Tech section, but when I had a problem with (I suspect) humidity rusting guitar parts in some of my collection, I applied a very thin layer of oil to the affected parts. Doing this just once protected them for many months at a time, which is handy because I'm kind of lazy. In my case it was the hex bolts that hold the string blocks in place on a few Edge-equipped guitars, as well as the Top Lock bolts, but I see no reason why this wouldn't work on your screws.
I used regular old 3-in-1 oil, though it may be called something else in Singapore. And a *really* thin layer, no big globs of oil. Good luck.