All of the hot dog rollers I’ve seen have no bearings in them, as such. There is nothing to oil or grease except perhaps the drive chain, but if you’re replacing parts, always throw in a new chain; they’re cheap.
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The rollers have teflon bushings at each end, that have a groove in them that goes into the sheet metal sides of the unit. It’s really a goofy setup, guarenteed to fail. There should be a real bearing on the drive end tube that one could replace. Other than the motor/gearbox, there’s nothing much to them. The heaters last forever.