Hi Rachel. If this is the sprinkler you're talking about.
http://www.rainbird.com/diy/products/sprays/dualspray1200series.htm
I did a repair job just today with these sprinkler heads installed. I took one apart and looked at it closely. I can say with 100% certainty this is another one of RainBird's less than adequate products aimed directly at the doit yourself homeowner. The name RainBird used to carry a lot of weight with me. But over the past few years they have put their name on some to put it mildly, "crap". I guess making a buck is what makes the world go round. I don't expect one of these heads to last anywhere near as long as the buyer would hope. Don't get me wrong. I do install the RainBird 1800 series and highly recommend them.
One more thing. These particular heads I worked with today had the RainBird undercut nozzles on them. Now those I like. If I were still in the installation business I'd use them exclusivly on my popup spray heads.
If I can't fix it, it's broken!