I was going to say WD40 too but thats just a quick fix. You need to have the dealer regrease the door. That will last a lot longer and you won't have to keep spraying. BTW the White Grease from the Dealership is amazing, I'm sure its the same stuff from the autoparts store but I don't have to pay much for it so I just get it here. Anyway I put it on my rear sliding glass door at my house because it kept getting stuck and even with all the rain and humidity I have not had to spray it for 3 months which is great. WD40 I had to spray 2 times a week.