I worked in a shop during the 70s and kept by 5-inch grinder. When I bought my 51 I dug the grinder out and it was froze up solid. I took the motor assembly out and soaked it in WD 40 until I could turn it. More WD40 and more turning freed it up to the point where I thought it would run on air. I put a fitting on it and it gradually got up to some speed.
I took the motor out again and submerged it in mineral spirits and got a ton of rusty sediment in the pan just by rinsing it. I filled the handle up with mineral spirits and ran it a couple times until the solvent ran clear. A few drops of oil and it works like new.
I'm sure the bearings wouldn't pass QC even in China but she works like new. No idea what brand it is but I bought it around 1970 and it has Made in Japan stamped on the handle.
