I think unless you use a high grade commercial panel, all main breakers are crap after 45 years. It all depends on the environment. Damp basement or garage. Water dripping into panel. Heat from the boiler. I look at all the new main breaker panels and question the QC of them.Those main breakers are junk, they are notorious for going bad. Last time I seen that exact breaker was in a Crouse Hinds panel that the bus bar was burning up. I think I seen it in an old Murray panel as well.