Help - Narda Relay - how do you remove the cover?


While working on the Mast head preamp I noticed the + and – connectors on the relay were lose. By the time I removed the relay from the box one of the internal connecting leads had broken off the terminal internally  and the wire had fallen back into the relay casing.  Both connectors have fallen off the casing.  Not sure why as all connections use use light wiring.
Attached are a couple of photos that show the problem – I am reluctant to, initially use brute force, and have a distant memory that some sort of solvent is required.
Any ideas please

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