The marks on the screen are caused by oil and grime transferred from fingers to screen via the keyboard. iKlear or any regular eyeglass spray plus *gentle* buffing using a lens polish cloth will remove most of the marks. You might have to be persistent and buff *gently* for a few minutes to get rid of grime that has set in.
If that doesn't work, my guess is that you might have left the dirty screen uncleaned for so long that the oils/grime have etched the LCD. Unfortunately, I don't know of anything for etched/scratched LCD screens.