Zinsco panels are known for having the buss burning at the breaker connection. One advantage that these panels have is it is very easy to replace the bussing if you can get a hold of an old panel. The was at least one company selling replacement busses but I haven't seen them in a while. Another trick that can be done is to trade the 2 busses with each other. This puts the bad spot in a position of the main breaker that there is no connection.
I would recommend you find someone to help with this repair that is experienced with Zinsco panels. Remember that the line lugs are still hot on the main breaker when it is off.
In my area there are probably Zinsco panels installed in homes than all other brands combined. I have a few hundred Zinsco breakers and some extra busses to use for repairs.
