Do you mean the part in the headliner that has a handle you can slide open to look out the moon roof(which is a glass sunroof)? what is the Model and Year of the car? By hard to slide do you mean just takes alot of effort to close it or does it actually get hung up and you have to jiggle it to get it to move further?
1991 Ford Taurs SHO 5 Speed White on Tan
1996 Chevy Lumina LTZ Rep 3.4L
1992 318i Coupe parts car
1992 325i Ls1 swap with a T56 6 speed 12.2 quarter mile
1976 Mercedes Benz 300D with a Ford 5.0L Fuel Injected soon to be Modded I am Captain Obvious