Last Sunday I painted the dome of the W15GTI black using Rustolium semi-gloss black. (I just couldn't take all that advertising continually looking at me through the grill cloth.) There were really no problems other than the first coat was a little blotchy..., but it was too shiny. After 96 hours I applied a second coat (can says 48 hours), but switched to an OSH ultra-flat black.
This covered all of the white printing just fine without problem and looks good. HOWEVER, the orange !JBL square is a DECAL! This second coat created a reaction with the decal causing it to rise and crinkle. It's not too bad, (and won't show through the grill), but in a few day, I'll try to use a light brush to remove the crinkle and give it another shot.
The lesson is don't paint the orange decals!