MX 6200 color shift

I have an MX6200 I've been working on that is giving me fits. The yellow is shifting about 1/4 inch to the front frame side of the page. The machine got a full pm including rebuilt transfer unit. I cleaned everything I could get to in the LSU. Nothing changes. I still think laser, but would appreciate any input I can get, as I don't want to order a laser and have it not be the problem. It's probably something simple and stupid that I've overlooked, but I'm out of ideas

Thanks for any input. Remember, it's shifting to the front frame side, not toward leading or trailing.