Do the pre-facelifts have seperate ballasts and igniters? (not overly familiar with the pre-face lift internals) You could have a ballast on the way out. I assume you made sure when swapping bulbs that they were seated correctly?.....I know that sounds trivial but even if its off a hair, can have massive impact on the overall output as the arc will not line up properly inside the bowl, thus making it dim.

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