I'm debating the same thing in regards to an oblique 'Reynolds 531 frame tubes' decal. I've almost decided to save what is left. In fact, I have already clear coated it, so the rest is not going to flake. Yours (like mine) looks like a water slide type. And if it is, a strong wind will eventually blow it off! If it is crinkly, the decal softener mentioned above is a good idea. Then you can either spray a clear coat on the entire tube after masking off the other tubes off to prevent overspray — or alternatively spray a puddle of clear into a small container and dip an artist's brush to paint the remaining decal out to within just a mm beyond its boarders. Should stay there indefinitely. And it will be original. And it will very likely not fade in UV if it has not already done so, something that may not be true of a replica depending on who made it and materials used.