[Radio Wrangler]

So long as the crystal and its evacuated envelope is OK there's nothing in there that shouldn't be repairable.

The foam is going to cop it however you open it. Things which would dissolve the foam might spoil other things given how long it may take to act. I'd try cutting around with a junior hacksaw blade with its little pin removed at one end.

You're in 'what have I got to lose' territory.

Very old crystals have done almost all ther ageing and if the oven is good, ought to be very stable.

David