Victor, I would say that even 20% is pretty bad, especially when the repair isn't something that the owner can do
themselves. But I have no way of knowing if that 20% is even accurate.
The mere fact that Kato redesigned the part implies that the failure rate must be quite high,
so I think 20% is a good guess.
Peteski, I think the fix has already been shown: Victor's collars.
The new part could have had the same diameter plastic axle tube, with the ends reduced a little, with steel or brass
rings snapped over the ends. Yes, it means a few more parts. But not much more. Really, the plastic
tube mold would have to be changed, and then there is an added assembly step to snap the collars on
But instead, they made a new bearing, new wheel center with a tab to lock it into the wheel rim, and they beefed
up the plastic axle gear too.
Golly, if they had just made the bearing ears a little bigger and the bearings them selves a little wider, even that would
have worked (but not as good as the original bearings

)
I understand, Kato had to make a design choice and a business decision: what was the most expeditious, "safe" way
to make a retrofit part to address this problem.
But I don't follow the reasoning that led them to the parts they made, and I am not at all happy with the QC they did
on the replacement parts, especially considering that they were making them to address a defect.
There are two other problems with the new wheelsets that I haven't mentioned because I was afraid it would be taken
as "too much bashing", but:
So far, out of 5 sets of replacement drivers, not only are they all too narrow in gauge, but at least one
plastic wheel center in every set has not been snapped all the way into the rim, making the wheel roll with a wobble
and making the gauge even more narrow. The rim can be squeezed back over the center where it belongs, but
this worries me too. There isn't much holding it in place and that is probably why some are coming through that are not
all the way on.
Second: On the geared driver.... All 5 of those on the replacements have the wheels mounted on the geared axle
such that they are not quite perpendicular to the axle. If you roll the wheelset on a workbench, you can see the flanges
wobbling in and out as it rolls. It is enough that the flanges will be in gauge on the NMRA plate at some points
around the rim, too wide at others, and too narrow at others. You have to "game it" when you regauge this one
so that every point around the rim is in gauge, even though some places are narrower than others. Yes, yes, I know,
it
functions, but come on. This is the sort of thing that might happen to me if I were screwing around
with one of my own engines and could only get it "good enough". But in a production part?
In a very back-handed way (I admit), part of the reason I am so hard on this issue is that this is a Kato product,
and I expected better. They are always so thorough, and so good at engineering and design, that I just expected
better.