Just got new 5er, previous one had decal disease and was a source of displeasure for DW. Have checked previous posts on care of decals but they were older. Older posts seemed to suggest 303 protecti...
Keeping it out of the sun is important. Other than that, the only factor that makes a real difference is the quality of the decal stock. If it's quality stuff (like that made by 3M), it'll be good for a lot of years. The cheap stuff (like on my Cruiser) will start to fade & flake in a year or 2.
Waxes & protectants just do not help much. UV is the enemy & to block UV, you have to apply something with pigments in it.