I've not had mine on the road long but ive been using 5W50 Motorsport or 10W60 Millers, no issues cant see there being any as they are in specification for cars designed to run 10w40 stock... which CA18s are
Personal preference really apparently better flow with an HKS my mate always ran HKS, im just running a Blue print filter at the moment as it was all i could get on the day i was changing the oil
if its brand new never been ran id be putting cheap shit mineral oil in for the first few hundred miles
I've got to do about a 1000 miles to run it in and have some millers for when that's done I'm guessing a semi synth won't hurt for running in,I just don't want to take any chances with the amount the rebuild has cost me