Russell I am not sure if this helps but the inspect NY site blames failure on aluminum parts while a past june NACHI thread seems to state magnetrip was copper.hmmm http://www.inspect-ny.com/electric/Zinsco.htm
Russ, back in the late 50’s and early 60’s Zinsco branded their panels as MagnaTrip, without seeing a picture I can’t be sure, but every MagnaTrip panel I have seen or seen pictures of was just a standard zinsco so I would avdise the client to have the breaker connections evaluated by a licensed electrician.