Please see evidence of issue below.
I am a long time player of the Forza series and I am aware of issues in the vinyl editor, such as region mapping and uneven offseting from right to left sides, and those are issues the community have found solutions for.
This however appears to be an issue with the underlying texture map for the car model itself, and is completely unavoidable. you can not cover this up with vinyl layers.
I have no idea if this is a recent thing, I know it was not a problem any time I used the car in another Forza, so i can only guess as to the reasons the map for this car is broken, unless the model was changed at some point. If you have any workarounds, solutions or reports on other car textures appearing broken i’d be interested to see if this is a simple error or a more wide spread issue.