Quoted:
Don't know about the trigger, but expect that while at Glock, they will remove your night sights and replace them with the standard plastic ones. Plan on it. You wouldn't get your sights back. Best to take them off before send it, or send only the lower.
I'm not sure where you heard that, but it is quite false. Matter of fact, the sights are just about the only thing Glock will leave on there if you send a gun in, unless you specifically request that they refinish the slide. If you send in a gun for refurbishment, they will completely replace everything except for the frame, slide and barrel. When they do that, they will return any after market parts you had in your gun in a baggy. Also, when you send it in for a function problem, they want the whole gun so they can function check it when they are done doing their repairs.