I have no access to any online image storage web site. I'll do my best to describe the leather handle.

Handle is composed of many chocolate leather slices compressed. Slices are identical dimensioned and finished to emulate a solid one-piece handle.

The owner says he has cleaned the knife by putting it in a dishwasher and run the cycle. He has also hand washed the knife in his kitchen sink using commercial dish detergents.

Present condition of the leather is a rough, fuzzy exterior with some of the leather slices fraying. Leather exterior appears to have white-ish particles embedded. I think this is undissolved detergent.

Overall condition of the handle is not bad. Handle's gross dimensions appear pretty much okay. The remainder of the knife - blade, hilt, overall integrity - is very good.
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As specifically as you can, please describe what to do to restore the handle to as close to when it was made as is possible. Also, how damaged will handles be after restoration? Would it be better to ask the maker to replace the handle? That would be expensive.

Is this a K-Bar stacked leather handled knife of other lineage?

I've done the following with older hatchet handles made of compressed leather.

Clean in hot lightly soapy water with a stiff bristle brush. Allow to air dry.

Fill a long thin glass, or other long tall container with neatsfoot oil and place the handle in to soak for a couple of days. With a hatchet, you have to prop it up. With a knife, it will probably stand on its own.

After soaking, let it drip dry and that is it. You can burnish the leather with a felt wheel to give it that shiny exterior or just use it. Use will shine it up as well.

Oil the handle occasionally so it doesn't dry out.

Jeremy

The stacked leather handle needs to be restored. This is what I do. It needs to be refreshed, new epoxy set, then reground and polished.
This is maybe 2 to three hours of work. I'll DM you with more detail