X2, epoxy filled coils also handle vibration better.

I think oil filled coils tend to leak if mounted horizontally. If you have to mount it that way use an epoxy filled coil. JMO

I've probably read as many opinions about this as to which is the best motor oil to use; however, I'm still on the fence. My better judgment tells me to use an oil-filled coil mounted horizontally in the original location on the manifold of my 55 Tbird.