Does it chip off in flaky pieces? Usually when there is a 3m bra you would see a delineation on the hood from bra transition to the paint. It is possible only your bumper was done. I've not seen what 3m does when it gets old and tired i.e. does it flake or peel..maybe someone else could answer. Possibly someone just sprayed some clear paint on the bumper. It is encouraging that the paint seems good underneath. Stop by a good paint shop, they could probably tell you in 3 minutes...the next thing is what to do about it
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