Vintage Disc Grinder Restoration [Hitachi Brand - Unknown Year]

This is vintage disc grinder from Hitachi Ltd Tokyo Japan. I found this grinder from the recycle shop in my city. It is 110V, 4 AMP, 50/60 Hz, 11000 RPM, Wheel Size 100. But I don't know the year of manufacture. So please share it if you know.
In this videos I recorded it step by step the process of inside cleaning & outside restoration.
I hope you find something useful & enjoy from this video!
I am happy to receive your feedback, advices, suggestions to improve myself.
!!! I make this video for just curious & challenge, so please accept my apologies if I have made mistake in this restoration !!!
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