I'll continue this thread and add some data points about "stacked leather handles" and rust. First the story.....
Being very fortunate indeed, just two weeks ago I ran across two old old old stacked leather handle knives from WWII: a Camillus Mark 1, and a Kabar Mark 2. Both were very very very rusty.
The Mark 1 had several washers which were cracked and split, but still in-place on the handle. As I gently pried on 'em to test em for strength, a couple of 'em literally crumbled apart. Since I can't leave well enough alone, I probed a bit more.... and more crumbled. I finally got to the point where 9 of the washers came apart before finding washers still intact and not split or cracked. Of Particular Interest was the material condition of the washers: dry-dry-dry. They made fresh toast seem soggy.
Of particular interest also was the amount of rust on the tang: lots and lots of thick rust. So I got out the electric drill, put a wire brush into the chuck, scrubbed down the blade and visible tang, then wiped everything down.
To fix this mess, I mixed up a large amount of JB Weld and proceeded to JB Weld the washers back into position, then JB Weld'ed around the perimeter of the broken washers to hold everything in position.
Bottom Line for the Mark 1: the handle is now functional, and there no doubt remains lots of thick rust under the washers I did not remove.
On to the Mark 2. It had 1-1/2" of missing leather washers on the handle, from the guard back. All the remaining washers were in good shape. But lots and lots of thick rust on the exposed tang. It received the same wire brushing, and I JB Weld'ed-in a few slices of wood to make the handle repair (yes, I agree: one of these days I'll remove the wood and do it right with leather washers.... but not today).
OK, what did I learn and what opinions have I formed ??
1. There's gonna be lots of rust on the tang.... thick thick rust.
1A. Can we do anything about it, or prevent it ?? probably not, ya just gotta expect it and live with it.
2. Will the rust degrade the function of the knife ??
2A. Not in my (humble) opinion. Though the rust was thick, the tang thickness was not appreciably degraded to a point of danger or uselessness.
3. Will the dried-out washers be a problem ??
3A. Not in my (humble) opinion. As long as the washers remain tightly in-place the handle integrity will be OK.
3B. If you pound directly on the washers, or otherwise abrade them, then yes, this will probably crack/destroy the washers.
3C. If all you do is grasp the handle in the "normal" fashion of grasping a knife handle, there won't be a problem.
As for an opinion about Leather Washer Handle Maintenance: I would say, YES !! Do something to maintain the suppleness of the leather washers. Don't let 'em go stale and hard and dry.
A. I'll keep mine soaked in Neatsfoot Oil.
B. I'll give a try to finding some Viscol (thank you Whitehorn !!) and mix it up with Neatsfoot Oil for waterproofing and see what that does.
Cheers,
Carl