Ive used a pressure cable oiler for years now on every bike I’ve owned, just good old 3-1 oil seems to work. I’ve been lucky that I’ve not had one break. By keeping the cable well oiled i can usually tell if it’s getting worse for wear. Before the pressure oiler I used to take them off the bike and using a lump of kiddies plasticine I formed a funnel which I filled with oil and hung it up until it runs out of the other end. The beauty of the pressure oiler is you don’t have to remove the cable and the jobs done in minutes. Having said that I’ve probably cursed myself and it will break next time out in the middle of nowhere