The Kroil that Michael Petrov mentioned is a good penetrating oil and rust stopper. It might be wise to let the small screws have an application to soak into and loosen the threads. I don't mean douse the area, but a light application that will wick into the threads. I find it works well if let to sit for a day or two.
Thaine

It ain't ignorance that does the most damage, it's knowing so derned much that ain't so! J. Billings