No Livro da Água, pg31 eu encontrei uma barra lateral:
Peasant Weapon Quality
Compared to the weapons crafted specifically for
samurai to use in battle, peasant weapons are generally
of much lower quality. Many of the peasant weapons
in the L5R 4th Edition Core rulebook include rules
to represent this. For peasant weapons which do not
already have such an entry in the core rulebook, a good
rule of thumb is that the weapon will break if it does
more than 20 points of damage in a single attack.
This is not to say that peasant weapons are all fragile
or shoddily made. Many of them, especially those crafted
from metal, can last for many years or even decades of
hard use at their intended tasks. Peasant blacksmiths
take as much pride in their craftsmanship as any other
Rokugani, after all. Moreover, they could if necessary
craft peasant weapons with much more resilient
components. Even a parangu can hold up better if it is
crafted from higher-quality steel. The GM should feel
free to modify or ignore the rules for peasant weapons
breaking if the circumstances seem appropriate.
Caso contrário, não encontrei nada específico para durabilidade de itens além de Great Clans pg31 onde eles descrevem estruturas de feridas / redução. O Livro do Ar pg176 inclui sugestões de maneiras de incluir os chamados arremessos nos ataques, o que tem derrubado itens (assim, realmente acertando a arma em questão). Caso contrário, eu não encontrei menção, nem mesmo na Forja de Arma Alternativa em Segredos do Império pg240