Polishing a Micro Seiki RT 3000G Gunmetal platter

I may have misinterpreted the question.  but looks like you're getting a variety of anwers.  Good luck. --Jerry

Well, the OP didn't say what condition the platter is in, so it's hard to know what it needs.  What you recommended is on point if the platter is a little more worn than just lightly oxidized.

Lets rephrase the OP's inquiry.

I have recently received a Imported from Japan Micro Sieki BL 111 Turntable.

I am keen to keep it aesthetically appealing, as this Model has a used market value of between $4K - $6K.

I have a Platter which is in need of being returned to a Highly Polished Finish.

Can a method to achieve this be recommended? 

??? I have not revealed my experiences or competency levels to achieve this as a  finish by myself as the option.

That's a nice piece of gear ... follow @carlsbad2 's advice and you will be long-term happy

Start with the simplest and least aggressive method of polishing and see if you get the results you want.  Personally, I would start some metal polish and a clean micro fibre cloth. 

I agree with @testpilot   Unless it's been left out in the weather for three decades, I’d be hesitant to take anything resembling sand paper to it.  Pick up any metal polish (check the auto parts store) and combine with elbow grease and a bunch of old sacrificial T-shirts. They’ll turn black as you remove built up oxidation but the platter should shine up nicely as you hand buff it out. A light coat of automotive wax will keep it shiny for a long time.