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I think breaking at the head/bend suggests movement and 'fretting'.
The only time I've used spoke head washers has been when building coaster brake hubs as they have really large spoke holes. Done a couple and given them dogs abuse and never had any breakages.
I just used the same spokes I normally would (Alpina, Sapim race, that kind of thing. Cheap, butted spokes). I probably just didn't think of using thicker spokes but my ack of issues would suggest they aren't really needed.
lynx
M_V
Spoke head washers then. Did the currently broken spokes go at the head/bend?