Hi all, thanks for your replies. The first one I bought was an after market since it was cheaper. After that one failed I decided to get the Yamaha one, now that one has failed so I got another yamaha one. Not sure if it's something I'm doing during the installation, maybe using the RTV gasket maker to help seal the crank case gasket? That might have something to do with it. I know some always oozes out of the side, so some must do the same on the inside.
I've also heard moisture damages them, and I ride in the rain. But I would think if any water was getting in there it would do more damage than just the pickup coil.