Thanks to everyone for the advice. I'm going to speak to my mechanics about each of these diagnostics. I'll post the results and hopefully, the fix.

Hi Ramon. Did you ever determine the cause of the problem? I've purchased a 1952 Packard for my father, and two mechanics can't figure out why it won't start after the engine is hot. One insists it's the starter (which we just had rebuilt), and the other mechanic is stumped and can't find an answer. Please let me know if you've found a cause/remedy. Thanks!