RB300 binding in horizontal movement

I've had my used Planar 3 for a few years now with a tweaked RB300. It was rewired with the incognito wiring kit and the expressimo counter weight and stub. About a month ago the tonearm started to bind during it's horizontal movement. It's as if the anti-skate has been set to 1 pound. If I move the tonearm about half way across the platter I hear a slight click and feel the binding give way. After that all works well and there is no resistance (other than the anti-skate setting) at all. The next day, it all starts over. I haven't done anything to the tonearm and it just started without any warning. Any ideas what is causing this and more importantly, any solutions to this problem?

Thanks.