When I bought my GXP last fall the headlights were in rough shape. I wetsanded, polished, etc and they looked better (not perfect) and quickly were weathered again. I plan on replacing them and have been reading up on doing a retrofit. I was looking at Rockauto and noticed they have 3 different levels of the TYC replacement headlights. "Regular Inventory", "NSF Certified", and "CAPA Certified". What's the difference. Is it like airplane parts where the part is the same and you are paying for the stamp on it or are there actual quality differences? I know members here have had many headlight assemblies apart and was hoping someone had dealt with these and could clarify.