So as far as I am aware carp can not detect oils they have no receptors for it, what they can detect is the lipids and any micro nutrients that are dispersed into the water as the oil rises off what ever its attached to.
Which oil is best ?, well can depend on the time of year when the water is colder i would stay away from fish oils as the congeal in the cold water and will leave a fatty residue all over what you have coated or soaked in them, best test is take your oil of choice and put a little bit in the fridge and see what happens to it. I have also listened to something recently that suggest it doesnt really what which oil you choose as they all have a good lipid content and its the other things oil can bring like being a converyor for other items that you have mixed it with like lifting particles into the water column. You dont need to pay carp tax for a good oil, the supermarkets crry plenty Good Hemp Oil and Toasted Seasame Seed Oil are 2 that I use.
Some of the other liquids are Hydroylsates and shouldnt be confused with Oils as they are very different but they can be mixed together to create a good effect for drawing fish to bait.
Cloudy liquids, just find a combination of liquids you like and get some condensed milk from the supermarket and mix then together will cloud th water up a treat.
If you use the Cap Oil make sure you wash your hands before going to the toilet šš