Windows are difficult to close.

Hello, my windows use a 2740 S385-28. They are extremely difficult to close down--I have to hang on them! I am going to switch to the same PN but 2730 (sash weighs 19lbs exactly). However, several of my window sashes seems to move at the top (side to side) enough that when I install the sash and close down, it misses catching onto one of the window balances and only hooks one side. Besides replacing the top sash guide (18-008 seems to be the correct top sash guide), is there any way to fix this? Something like centering or buying top sash guides that stick out further?