Steve those connectors are rated at 30A I'm not aware of any alternative bullet connector in the civilian market that can fit. Incidentally the smaller ones were originally rated at 10A but increased to 12A, certain types of commercial bullet connectors can fit, but the real thing is not that rare.
The distribution box has no fuses, they are circuit breakers that require some sustained overload before they trip. Although when they do trip they do not break the circuit completely as there will be a residual voltage due to the winding still being in circuit. So a tripped or failed breaker may exhibit full voltage on a multimeter but due to the resistance the winding this will drop to very little once some current is drawn by a load.
It is sometime since I have taken one apart. The most likely cause for failure is if moisture has got in & caused corrosion, but if it looks clean & doesn't smell charred. I would leave alone for now rather than make work for yourself. I have resistance readings if you want to test it before embarking on a dismantling exercise.