Sliding back window gets Stuck

I've had my truck for almost a year and I never opened the back window until last week. It took everything I had just to get it open and to close it. I checked to see if something may have been down in the seal but everything looks fine. Just wondering if there is some kind of lube or something I can put on it so it will open and close smoothly.

 

Silicone spray

 

OK I'll pick up some tomorrow.
Thanks

 

If you haven't already done something for this, I would recommend powdered graphite lock lubricant as opposed to any kind of wet lubricant. Poof some graphite into the window channel, open and close is a few time to work it in there, then vacuum out the excess.

 

I have had my truck for over three years now and don't remember ever opening the back window. I think I will check it out this weekend.