Grey spots in iPhone 3G 16gb Display?

Hey Guys, I got a Used 3g 16gb Iphone that is in reall god shape, but the screen has some grey spots on the upper part, maybe 3/4 inch under the top part of the screen. I've noticed that the biggest spot (they are pretty much like lines instead of dots) is getting bigger or smaller within days passing by. I've received this phone with the money to change the display, but i'm looking for other solution as i have already spent the money! :D

I've read in many forums that this could be humidity and that it can be fixed just taking the display out and cleaning it with the iphone cloth that came with the first series (i still have it)... do you think that this would help? or should i get a new display to change it?

Cheers!

Max from Mendoza, Argentina!