Block crack - is this terminal

[Bob Culver]

Decades since I did it. Had no fancy tools. Would have cleaned the metal using a small grinding wheel in electric drill. Used a plumbers petrol iron with generous size bit. (In recent times have used large hand solder bit clamped to a propane gas torch). Woud have used Duzall flux. 50/50 radiator solder would be nice but probably used 60/40 plumbers solder assuming still available. For such a thin section the heat can be conveyed mainly from the bit, avoiding direct flame contact. Once tinned the solder can be built up in dabs. 
The ends of the cracks ideally identified and small screws fitted.
If you can make up and attach a cover a neoprene or cork gasket alone may suffice. A neat cover plate with countersunk screws would add character.