Bodywork decor strips

[hoover33]

The body work S2 detail tranfers are detaching themselves from the bodywork on both sides of the car in exactly the same place, just behind the front wheel arch where it curves into line up with the rest of the car.
A few qusetions :-

1. What is considered the best stuff to stick it back . It's on attached both ends, just detached on the curve. I am looking for something that will stick the transfer back, but will not smear on the paint work so that it can not be removed.

2. Why is detaching. I have wash the car using Turtle Wax Extreme, and occasionally use Merr. Or is just old age.

I really want to keep these decors, as like the car in its original get up