I don't know if toolheads have always been this way, but they seem to cycle through maintenance machines as though they were intended to lose durability at some point.
Now that we have %-type recipes that randomly give outputs, couldn't it work similarly to Krastorio Matter where stabilizers only have a 99% chance of surviving the crafting process?
I don't know if I could even qualify this as a bug, but I don't think anyone would mind merely needing to add toolheads to their manufacturing process for dirt farms.

Chance stuff like you are referring to was never a factor in Yuoki before.

Though it does make sense to do so.. a problem with this sort of stuff now is the new quality system in SA.
It would now be technically possible (even without chance) to upgrade the tool head during normal use.
This is actually something ill have to look into blocking because that would not make any sense at all.

But with that said having the tool head have a chance to be "destroyed" during use does make sense to have as a setting