It would be easy enough for someone who is unfamiliar with the arbor issue to be confused by the split washer comment, since putting the washer in the rear of the arbor actually would increase the length as well. But yeah, dropping the washer down the arbor hole in the barrel is why I sometimes lose it when I take the barrel off. If you've looked at Pettifogger's articles you understand the issue of the short arbor (or too deep of a hole in the barrel, whichever way you want to look at it), and the way he shows to fix it is the permanent fix. The washer is a quick'n'easy way that Coffinmaker had suggested. Really should be just temporary, but it works for me. I mean, I shot the guns without doing anything about the arbors for thousands of rounds, but the wedges started getting a bit loose and the fix snugs it back up. I also have never messed with the leaf hand spring and no problems in about 17 years. But, that was only maybe 3000 rounds per gun since I shoot others as well, and I don't practice. For serious competitors who will put the guns to hard use, the modifications will certainly have even more benefits than for just the casual shooter.
Oh BTW, I almost forgot, the washers go in my four '51 R-M's; my Type II which is less than a year old actually has very little gap between the arbor and the end of the barrel's arbor hole, and the split washer is too thick and won't fit in that one. I used a very thin flat washer instead, but even then I could only barely insert the wedge. I'm shooting it tomorrow without the washer at all (allows me to insert the wedge just a tad further) to see how it goes. Maybe Uberti is getting better about this issue? (Kinda doubt it, but who knows? Seems like not too long back someone mentioned getting a conversion or OT that he said had a good arbor fit).