Lexol is an excellent cleaner but is just that; a cleaner. Neatsfoot oil is not good for pure cotton or flax threads as it will decay them over time. OK for modern synthetic (what I call "alloy") threads that are a combo of natural plus nylon or rayon support threading, usually braided or hard-twist.
I've resurrected quite a few rock-hard leather objects from the Civil War era (cartridge pouches, belt packs etc.) using Leatherique, which is a 2-part project with separate applications. Part 1 is a penetrant/rejeuvenator that soaks into the leather and bubbles out all the crud that's accumulated over the years (centuries). For small stuff like holsters, you can slather the item with Part 1 and seal it up in a ziplock bag and let it sit for a few days. I like to throw the rock-hard stuff in the bag out on the deck for a few days in mid-July. The effect is just like a steam bath but without water. Really softens up the fibres to where they will bend on a fold like a lid, say, without breaking it off. After removing excess Part 1, apply Part II and work into the leather, maybe need several applications a couple of days apart. Let air dry; no sealing up like with Part I application. Wipe down after final application of Part II and you'll have a nice-feeling and good-looking restoration, even leaves a subtle polished patina on the piece. Part II app is a restorer and a finisher phase.
This is the best stuff I've ever used on rock-hard leather that's worthy of restoring. It's expensive but for my $ its the best. Google it for product details, factsheet, prices and shipping. KBM
