I think what may be happening is your new clear is still a bit soft, but the old stuff thats sat a week is more cured, so when you try to buff your blend edge, the new clear is tearing away at the edge as you buff, and the new and older clears are buffing different. Normally, you keep getting a halo you can't get rid of. You could try waiting or throw some heat to the new clear so it cures up more, and then try buffing. But really, you should of cleared the whole piece when you cleared the second time, instead of just blending it. Specially being motorcycle parts are normally rather small. I understand not wanting too much material build up, but you could have cut the whole piece rather flat, which would have taken some material off, before reclearing, and had a nice flat surface for you new clear to go on. Plus if you just blend your clear, you have an invitation for an early failure at the blend area, since urethanes the new will not remelt the old, and then you have little mill thickness of material at the blend area.
I am not positive, but I think if you did cut your clear on the piece flat now, and then reclear the whole piece, your halo would disappear. Just be very carefull around any edges, you will not want to go through the clear at all into your candy, or you will really have work ahead. Maybe go conservative and sand all with 800 wet or finer, and be real carefull if there is any sortof bodyline and around edges.