It is mentioned often that tru-oil ambers-up over time. Here is an example:
Kit freshly strung up in May 2015
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And how it looks now, late January 2022
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Note that the same colouring was used on the body and the REAR of the clear pickguard.
The body was finished with tru-oil, there's a build diary somewhere.
I know the lighting for the pics isn't the same, but the difference in colour is pretty obvious.

This is purely for illustrative purposes, make of it what you will.

Grant