My sunroof occasionaly sticks, especially at lower temperatures. In my case, the rubber has aged just enought to become very sticky. It still seals well, so I attempted several lubrications to ease it. First do not use lithium grease, after about a day it makes it much worse. My most successful attempt so far has been with dry graphite powder, in a tube. Get some from your hardware store. It may even be better to get the graphite powder mixed with oil, as its much easier to apply. This has lasted me about a month w/o problems so far. Spread it all over the rubber, & clean/oil your tracks. The problem should dissipate.
You may also want to check the drainage holes incase they have debris in them.
