Before you recommend I look at the long thread on tramming or go to YouTube, been there, done that. A bunch of times. This is a little different.
My Marke II Longmill is relatively new with only probably three of four hours on it. I am learning (and making mistakes as I go). My spoil board is nicely surfaced and that hasn’t changed. I have been surfacing some smaller pieces and having good results, until I started getting stripes in my work. There was an incident with a loose screw in the router mount. I fixed that and tram was clearly out with the next test cut - those telltale stripes. They were faint but noticeable and worsened. I noticed the v-wheels on the X axis were not a tight as they should be (I could get some movement front to back - small, but shouldn’t be there. I adjusted the wheels slightly and the fit for the wheels on the X rail is spot on. I have removed the router mount, cleaned and reset it. I ended up with a .25mm shim where the four M-5x25 screws attached it. I had not needed that before. That brought me within .002 inches (yes, two-thousandths) in both X and Y over a span of 4-1/2 inches (dual indicator gage). I think that much aberration is inconsequential, especially in the width of a 1" surfacing bit, but I am getting visible striations and can detect a line with your finger - even see it. The couple of pieces prior to this job were almost as good as sanded. They were gorgeous in fact. I rotated the cutters on my bit - same outcome. I changed the cutters totally. Same outcome. I bought a new surfacing bit. Same outcome. Same outcome whether I run the surfacing program in G-sender, or just use a pocket cut. My work piece is solidly fastened. No movement there.
What am I missing, or what would you try? Thank you for your ideas.