I agree with Brian!
Go to your local grocery store and buy a 500 pack of Q-tips. Use as many as you can in all area's of the sun roof to clean the old grease. Then go to NAPA or any other place that carries Sil Glyde or white lithium grease if your a OEM only guy.
Make sure the rails are clean enough to eat off of before you apply new grease, no joke about it.
The good thing about Sil Glyde is that its almost clear as compared to white lithium grease.