Its for safety. They don't want anybody spilling coolant or any other liguid for that matter on the track. Can you say spin out and crash ? Get a universal. It is best to have one even if you weren't racing. Keeps the coolant level topped at all times.
I used one from Summit. It's nice and effective. Wedges in pretty good. See pic front right and in front of radiator. It's tall an hooks up stupid easy. Had to make a couple brackets but hey it's worth it.