consult a saddle shop, one's recommendation
bill tindall
>I had this problem and found myself in Cody, WY where there is a shop that makes, restores, refurbishes or conserves saddles and the like. They work on saddles, some costing tens of thousand, and seemed to know about these things. Here is what the person recommended to me to clean, restore a very valuable carved leather belt......
If the leather is lacquered, which is common to protect it, remove lacquer with a piece of sheep skin wet with acetone. Gentle strokes so as to not skuff. Then again, using sheepskin wet with a soap they sold there, gently wash the leather (avoid scuffing) and finally rise with water. Presumably any saddle shop would have this or an equivalent soap. It was called BIC 1 and came in a black bottle. They had a second preferred product but it came in a needlessly (to me) large size only that cost a lot.
This part blew my mind. Then reoil with a high quality neatsfoot, or preferred, was olive oil. Small dabs of olive oil are applied and worked into the leather by flexing the leather. Oiling will darken the leather, if that is a problem. By dang I tried this on a brittle leather rifle sling and it softened it back to utility. It took a lot of working the leather to get it resoftened.
Finally overcoat with harness dressing which is a lacquer product. This is padded on with sheeepskin pad. Should be as easy to do as French polish (a little humor here).
One might imagine that this process applied to an antique saddle might cost some serious coins.
They didn't use any sort of waxing of the leather and expecially recommended against it for the carved belt (or saddle) as it would fill the carving.