Can anyone share if they happen to know if the plastic solenoid cover, (the little plastic or bakalite end where the wires attach) on a 56 Cadillac 365 starter is the same plastic cover that's on the later 60s GM starters?
Is the solenoid bolted to the starter body with some straps, or is it bolted to the starter nose with two bolts? Sometime around that year is when they redesigned the solenoid setup. Pictures of your starter will help us help you.
That looks like the "modern" solenoid, should be easy to find a replacement (but not just the plastic cap, you'll have to buy the whole solenoid assembly) It also might not be the original type starter, as the listing I found for a solenoid for a 56 Caddy shows the old style. But if you shop for a 58 Caddy you should be able to find it