Hey Kirby people: I just reassembled a Heritage I after replacing bearings, etc, only to find that there is friction somewhere in the speed switch. It won't fully release and hangs on in low speed. I replaced the two links with new ones. Same problem. Then I put in a new spring. Same problem. Where am I going wrong? Is the switch itself to blame? When the button is slid by hand, it feels easy enough, but something is preventing the spring from turning it off. Ideas?