You can use some polishing compound for ghost striping, it will help to blend/fade the paint together better... it can probably still be seen if you look at the area down close, but it should be way less noticeable from a distance. We just did this to Max's hood decal that was so deteriorated it was disentigrating!!
I just finished removing Tsukiko's pin striping we put on Kuro Neko when we got her, it was beginning to pull off anyway because the pin striping was old to begin with... a razor blade works well for getting underneath the edges to start pulling it off, took me about 10 minutes total. We just picked up new pin striping but haven't had a chance to put it on yet... Max suggested going over the area where the new striping is going with some rubbing alchohol which dries almost immediately and will remove any build up that might be present.
Now I would just like to strangle the idiot who re-painted the car and didn't remove the original pin striping!! grrrrrr.... not to mention they used a really rough sand paper and left deep gouges in the paint!! That's worse than ghost striping since the only way you can fix it is by repainting the car and stripping it down to a smooth surface!! Plus the striping went all the way around the car, and I don't like it across the front and back ends, the rest isn't noticeable when you get new pin striping over it.
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