Yep, mine failed too, after only three years. I couldn't find an OEM replacement, so I got a new Atwood RV model. It's rectangular, and wall mounted. I left the old one in place until I can come up with a decorative item to cover up the hole.
I have a friend who replaced his OEM Costar with a plug-in from Home Depot. Simple! I wish I'd thought of that!
2012 Itasca Meridian 36M
2012 Jeep Wrangler