Have ya thought about graphite impregnated bronze to replace them? You'd never have to lubricate them, and I'd bet they last a lot longer than plastic. If it's the wheels themselves, perhaps something with a ball bearing in it might be better suited. I don't like plastic bushings in anything that has to operate in dirt and dust, especially if it has to be stored outside when not in use.
How big a rake didja get? I'm thinking I need one to pull behind my LX for annual cleanup on the back side of my property. Needs to be at least 6 feet wide, but any wider, and I'm gonna have a lotta fun with all the trees back there. My problem is that NOBODY seems to be selling anything like that around here. Most of the used stuff I've seen at some of the 'local' auction houses is beat to crap and would cost as much to repair as it would to buy the implement new. Just haven't found the right person getting rid of the right implement at the right time, I guess. Those stars seldom align for me.