Welcome to the Community, @Commheat. Let me share some information about recording an item in your QuickBooks Desktop (QBDT).
Yes, I agree. You can record the purchase of the new motor by entering the item in inventory. However, I'd recommend reaching out to your accountant first. This way, your accountant can decide which accounts to use to properly track your inventory.
Making adjustments to a product's quantity is a common practice to monitor any change in the product count that is not due to a sale or purchase. This helps keep track of the inventory when items break or when there are discrepancies in the inventory count. For your reference, check out this article: Adjust your inventory quantity or value in QuickBooks Desktop.
If you use QuickBooks Payments and want to void or refund a payment from your customer, check this article: Void or refund customer payments in QuickBooks Desktop.
If you have any questions or concerns about recording a refund or other QBDT-related issues, please don't hesitate to comment below. I'll do my best to provide you with the answers you need.