Just thought I'd mention this because some guys say they've had problems with "stuck" caps and even damaging their keys.
Some of you may have an actual problem but I have a method that some of you may not know about.
I believe a lot of the problems are caused by pressure build up. If you try to open the cap under pressure by simply turning the key to 3:00 and lifting up, the pressure will cause a jamming effect on the key. So it's simple; just press the front area of the cap down moderately with your left thumb first and then turn the key to 3:00. As you lift you remove pressure. This relieves pressure from effecting the smooth operation of the key.
Works for me.