If you haven't read the changelog for 2.1.76 it is HIGHLY recommended that you do.

• Added minimum quantity back to Repair config

NOTES: I removed this last patch because I did not consider that server admins might be allowing users to repair items without crafting recipes (as of last patch mcMMO determines minimum quantity via counting ingredients in a recipe)

I'm sorry about making this change without thinking it through fully.

If you do not define minimum quantity in the repair config, mcMMO will grab the minimum quantity automatically as I programmed it to do as of last patch, otherwise if it is defined, mcMMO will respect that and use that for calculations.

The minimum quanitty should be set to the number of ingredients used to craft the recipe, for example 8 for diamond chestplate etc, you do not need to define this unless you are allowing players to repair custom items.