Sounds like the meter works. My hope is it's a dirty contact in the knob. Try spinning the shutter speed knob through all positions for a few minutes. If that doesn't get it working I'd send it in for a cleaning. In fact that's probably not a bad idea anyway.
This is what I believe the problem is as well. I had a Mamiya 6 body that did exactly as yours and sent it to Bob at Precision Camera Works in Chicago and he cleaned the contacts inside and around the shutter dial and its work perfectly since. Sounds like yours just needs a little cleaning. Call Bob!
Ok i tried spinning the dial a bit as suggested, and that seems to have done something.
Though I do notice now that if I use A and meter a scene, then switch to AEL and meter a scene without moving the camera I get a very different shutter speed reading. Any thoughts as to what would cause that?