I just had a look at your other thread... bad design.
Those original pulleys are coarser than the ones from ebay (that are used for 3D printers).
There is a marking on the belt (T5x165), like this one:
http://www.ebay.com/p/Milling-Machin...165/1138257840
I would replace the whole thing, both pulleys, with finer teeth and narrower belt. Important thing is to keep the transfer ratio (ratio between number of teeth on pulleys) the same.
Motor pulley has 14, how many teeth are on the other one?
Since the motor shaft is short, I would use the pulley with 8mm hole, and made the bushing long enough to match the 5mm shaft and have the proper contact with screw. I would even glue the bushing with epoxy to the motor shaft.
I would probably even consider widening the original hole on 14-teeth timing pulley, to suit bushing.
Bushing could look something like this:
https://pengeapens.myshopify.com/collections/bushings
or this:
https://www.pennstateind.com/store/PK-PENXXBU.html
Or just a simple hollow tube, 5mm inner, 8mm outer diameter - they can be made very precise and absolutely concentric, and material can be even plastic (Acetal is ideal for this.. or PVC).
SPD/SI have a
calculator for timing belt diameters, distances etc... very useful for determining the belt specs.
And I wouldn't worry about warranty.. you can always put back the original parts.