I have to admit to another longtime mispronunciation, of which I was reminded tonight.  My only defense is that I'd only heard it correctly pronounced once, and was so certain it was wrong that I looked it up.  To my shock, the misprounication I was seeking to disprove was actually a long-lost correct pronunciation.
Incorrect:  Mars-CA-pone.
Correct:  
MAS-car-pone.