[Outwest34au]

The silver tin unit looks more like a bi-metalic thermal circuit breaker to me. When load capacity is exceeded they open the contacts and prevent current flow.
They are well known for gradually failing over thier life. May start as 30 amp then decrease over time as the metal strips weaken from moving open/ closed, plenty of cars use them on headlights and youhear reports of hi=beam going on and off when bigger wattage globes are fitted.
A replacement option could be a relay holder with the fuse built in on the side, they look tidy, are compact, cheap and use a standard blade fuse. That way the existing relay wiring could be transferred to the new case and probably only need to change the terminals on the thermal bit.