Hi Michael,

Here is a previous thread answer to your question which I thought was right on the michael.

* Posted by coho z8/9 N. Calif (My Page) on
Thu, Aug 11, 05 at 21:59

Get a tube of silicon grease and lubricate the plastic cam and follower (The part that makes sprinkler oscillate) Also the seals/bearings, on the ends of oscillation tube need to be lubricated. Mind, this will only extend service a season or two. They are built with sales in mind, not use.
Aloha

Thanks, I'll try it. It only seems to happen once I've been using it for a while (and it's new!), but I'm willing to try anything.