Or repairing weapons, tools (not vehicles) would lower the durability of said item, once durability is 0, item is broken and can not be repaired, (can still salvage) this would make crafting more lucrative. it would also help with traders offering higher tier items than you can craft, you buy it, repair it x times and it breaks, you have to hope they offer you and better item than you can craft or crat the ones you can. (this would give more incentive to loot weapon/tool parts as well).
Eg - in my game im using knuckles. I can craft up to iron tier 3, but i got steel knuckle parts and already got steel knuckles tier4, no point in me looting more steel knuckle parts or the knuckle books anymore, with this change I would need to continue to find parts and books.