Color Pro HX Lamp optimization puzzle

I'm replacing the MSD250/2 bulbs in my Color Pros as well as doing a thorough cleaning and the lamp hotspot optimization is being a bit of a bear. I loosen the alignnment thumb screws and can get things pretty even but when I retighten the screws the bulb jumps back to about where it was when I started the procedure (typically a hotspot high and to the left). The bulb seems well seated and everything seems clean. Any other ideas or things I'm missing?

Thanks,

Joe
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