Denatured alcohol or brake/parts cleaner and then compressed air work for me. If using brake cleaner make sure you have all other areas and materials removed (stock) as it can discolor or eat into plastic. Verify your threads are good on the screws and run a bottom tap in the holes. If you don't plan to remove the rail, you can go with a more permanent loctite as well. Also ensure you are torquing to specs. One other thing, shake the bottle of loctite for a coupel of minutes before you use it to get it mixed. Good luck.