Cleaned gas hob - wrecked a part but what is it?!

[Orangealien]

Aargh - I wanted my kitchen to look decent for visiting family so cleaned the hob. Round each of the gas burners, if you lift the top solid circle bit off, you can then lift off a silver/aluminium(?) ring. I put these silver rings in the dishwasher as they had brown stains on them and instead of coming out sparkling, they have come out matte grey (all silvering lost). Now I wouldn't much care about the colour change but when you touch them, black stuff comes off on your hands. And, ridiculously, the brown stains are still there

I was thinking of replacing the rings but the finding serial number (Neff) requires the entire unit to be lifted out of the fitted kitchen plus even if I do that the hob is almost 20 years old and neff doesn't carry spares that long.

Housekeeping is frustrating. Any advice please?

I did this with Oven Pride a couple of years ago, not meant for aluminium ring burner things apparently. They still emit a silvery dust all over the rest of the cooker. No help sorry.

I did this to my stand mixer attachments. When I rang the manufacturer they accused me of putting them in the dishwasher (moi? Never)

They told me to rough the attachment up with a scourer then coat with lemon juice and wash by hand in future.

Gobsmacked but it worked for me may be worth a try ?