An interesting topic notwithstanding it has been all previously covered but I suspect we all modify our approach based on our own experience.

For example I have almost completely moved away from using a tumbler and ultrasonic cleaner. The results, for me at least, were not forthcoming.

On metal parts I first use a 12L parts cleaner with water soluble concentrate to remove grease & grime and then if needed and irrespective of rust soak in Evaporust. I find this product restores the plating finishes to their original sheen. Naturally any rust is removed most effectively.

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On small metal parts I use a combination of a wire brush on a bench grinder or, for example, in the case of jones plugs (male & female) a wire brush within a dremel tool.

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For plastic parts, mainly posts, I use dishwashing detergent in the sink!

dhutton it seems that the oxidation on your machine is fairly severe and to be most effective a fair degree of disassembly will be required. But it is surprising how quickly you can move through it and the results will give wonderful personal payback.

I guess, depending on the environment, that can certainly happen again. On particular parts that are prone to rusting eg lockdown receivers, rear side of lockdown bars, tilt housing etc after evaporust rust removal I clearcoat the part. This seems to eliminate/minimise rust returning.