By splitting them I assume you mean breaking the seal and opening them.

Suggest you add year and engine size to your signature. It will help with this and many other questions you might have in the future.

Sometime in 2002, I think it was August, BMW changed how the lights are sealed. Prior to that date the light housing could be opened with heat. Some baked then in the oven, some used a heat gun, isn't easy but it can be done. I used a heat gun. After that date the housing seal is much different. Heat does nothing. They can be opened but it is a very long tedious job to get it done. I have opened the later type and I won't ever do it again. I had one of each version when I opened them.

On the upside, you can add angel eyes and modify the lights while you are in there.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas