Darkening is normally due to moisture ingress you are right, so new gaskets all round, properly installed after the surfaces are inspected would be a great start, followed by a low level pressure test to see if they are doing a basic job. I don't know of anyone reversing the darkening but there are some good relumers out there who can bring it back to whatever level of brightness tickles your fancy.
Nice Vaders by the way. I have a Stormtrooper waiting for me to get round to sorting it. It has many issues so it keeps getting bumped down the waiting list to make way for more promising projects.
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