If you play where it's dusty, clean it and re-lube it after every game.
If you're not sure what a properly cared for gbb looks like, use green gas instead of propane for a while. Then you'll know where/how much the lubrication is supposed to be at. Until you know how to lube the gun, green gas will be better for you, although propane is significantly cheaper.
If you take care of it, and clean it every once in a while, it will treat you right. I have a WE MEU that's been going strong for almost two years now... still hasn't broken.