WD-40 is not a true lubricant, it’s more of a cleaner. It’s great for penetrating stuck bolts or scrubbing rust but not for oiling moving parts. It dries out quickly and does little to protect wearing parts. For a sewing machine “light machine oil” or even just purpose made sewing machine oil is the correct option. When it’s used to “refurbish engines” they’re removing dirt and rust, while likely also polishing pitted areas. They will clean off the WD-40 afterwords and use motor oil the rest of the time.
WD-40 is not a true lubricant, it’s more of a cleaner. It’s great for penetrating stuck bolts or scrubbing rust but not for oiling moving parts. It dries out quickly and does little to protect wearing parts. For a sewing machine “light machine oil” or even just purpose made sewing machine oil is the correct option. When it’s used to “refurbish engines” they’re removing dirt and rust, while likely also polishing pitted areas. They will clean off the WD-40 afterwords and use motor oil the rest of the time.