I agree with fatcat, at this point I'd have stripped the whole thing down and checked the fit of each screw in their appropriate holes then once they can individually be fit in place on the part directly take them out and reassemble everything except those screws (dry fiting is putting together without fasteners or adhesives) and make sure they line up correctly then screw each screw in about half way in a cross pattern (screw the upper left, then lower right, then upper right, then lower left) until they are screwed all the way in.
Also, I would suggest cleaning it out with a tooth pick and alcohol since alcohol will evaporate more completely than any lubricant such as wd40...also, if there is dirt in there and you use wd40 to clean the hole you'll risk basically gluing that dirt in the hole...the toothpick will make it easier to pull things out if there is large chuncks of plastic or something in there. Then, once you are sure it is free of debris you can apply some wd40 to help make the plastic more maluable
Also, I would suggest cleaning it out with a tooth pick and alcohol since alcohol will evaporate more completely than any lubricant such as wd40...also, if there is dirt in there and you use wd40 to clean the hole you'll risk basically gluing that dirt in the hole...the toothpick will make it easier to pull things out if there is large chuncks of plastic or something in there. Then, once you are sure it is free of debris you can apply some wd40 to help make the plastic more maluable