If it's only the print moving, and not the vinyl, especially if the edge is looking like stairs, or large pixels, then the encoder scale and/or encoder reader are dirty/damaged. Likely just dirty. The encoder scale is about 1/2 inch tall sunglasses colour strip of plastic running behind the steel drive cable that pulls the heads along. get a flashlight, and light up the wall behind the strip, so you can see through it. If the colour is fairly uniform you should be able to clean it, if it looks like a city skyline then it has delaminated and is done. On that note, only one side of the strip is exposed, while the other is nestled in the track, and you can flip it over if one side is still intact.
For cleaning it, a soft rag or shopcloth, isopropyl 99% alcohol and reverse-credit card it, so you get both sides. it works by shining a light through it to read the perforations, so don't just clean the front. Also dont crimp it, if it gets a fold line it's done.
If it's the vinyl coming out on a curve thats a different story, likely one side of pinch rollers biting much harder than the other, or howerever the roll is loaded on the back could be crooked.
