Hi, cloren.
As I have understood it, the epoxy just keeps the internals in the cover and protects the possible active circuitry etc. And is a PITA if something gives

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The coils should be wax potted if the stability of the coil is a concern. Hot wax fills the coil completely, also altering some tonal characteristics so it might have unwanted side-effects.
Obviously I might be wrong, and water-like epoxies are used nowadays to pot coils. I'm sure there will be other people chiming in

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Just my 0.02€
Sam