[Exxy]

For the purposes of repairing your weapon, two things come to mind: you can either repair your weapon at a Blacksmith or use some repair powder if you keep any on-hand for such an occasion. Currently though, it seems once you hit your normal max for Durability on a weapon (in this instance 42/42 - meaning when you try to repair the bonus Durability from Sentimentality it will be 42/52 no matter how much you use), it won't repair it any further unless taken to a Blacksmith.

Example:

You use the Repair Powder.
You use the Repair Powder. Your Blacksand's condition improves. (42/52)
You use the Repair Powder.
You use the Repair Powder. Your Blacksand's condition improves. (42/52)
You use the Repair Powder.
You use the Repair Powder. Your Blacksand's condition improves. (42/52)

[Neus]

This should be corrected.