I cleaned up the mech board on my Grand Prix last summer using a bucket of water, some diluted super clean, and a soft bristled paint brush. It came out quite nice.
This is what I started with.
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Washed everything with the soapy solution and a brush.
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Rinsed it all off with a bucket of warm water. You can see how much dirt came off!
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Then set it out in the sun all afternoon to dry.
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And here it is reinstalled in the freshly painted cabinet. I still did a little special cleaning on some of the switches, and stepper units after this pic was taken.
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If you're careful in your cleaning you won't damage anything. I was very cautious, and deliberate when using the brush.
Hope this helps.
-Paul