Personally, I was going to recommend PURE neatsfoot oil, but that has been argued to death here and elsewhere. Suffice it to say, whatever you use, apply lightly, nothing worse than drowning the leather. Apply after a careful washing with good quality saddle soap (no silicone) and, when almost but not quite dry, apply the neatsfoot oil with your fingers, rubbing in well.
And be sure to avoid anything with petroleum products as part of the ingredients. Here in the USAingredients are shown on the container so you can tell what you are using. No offense to saddler, many hide foods and leather dressings available here in the US contain petroleum products or mineral oils and will, after a long period, destroy the leather. They are good for user grade items but should not be used on collectible items that you want to last indefinitely.
Saddler, I am glad you mentioned Ko-Cho-Line, I have used it on some of the items I make for reenactors and do find that it seems to work well. The can does not show any information about what the ingredients are. Do you have any idea what it's made of? I bought it from our Mennonite harness maker (my mentor in leather work) about 15 years ago but he never restocked. I may be interested in more for the reproduction items I make.