I’d try to find an OEM/NOS gear before switching to metal.
That plastic gear was probably used for a reason, and replacing it with a metal one could potentially transfer the failure to the mating gear, shaft, or another part of the water-pump drive. On a restoration I’d rather have the correct sacrificial part fail than introduce a new weak point somewhere that is harder or much more expensive to repair.
I’d search the part number through old Honda dealers, vintage MX suppliers, dismantlers, eBay listings, and CR125 owner groups. It’s also worth checking nearby model years because Honda reused plenty of parts, and sellers do not always mention every compatible model in their listings. I treat game libraries in a similar way. On [Slots Palace Casino](https://slotspalace-deu.com/) a title might appear under different filters or collections, so searching by the exact game name, provider, theme, or game type can be more useful than assuming it is missing because it is not visible in one category. Slots can also differ by mechanics and visual style, while live games are usually organized separately. Cross-checking the Honda number against a parts fiche could save you from buying the wrong gear.
If you still have the broken gear, definitely compare tooth count, shaft fit, diameter, and thickness before buying a used one.
$100+ hurts for a small plastic gear, but I’d personally choose a good OEM piece over an unknown metal replacement.