It was a merchant ship, not a US Navy warship as you said in your first post. Merchant ships ran blockaids all the time. There was big money in it.
If it was a merchant ship, then WHY did the US demand payment of the price of the ship 20+ years later? If the merchant ship was doing something illegal (which it was by having the Mexican official aboard and running guns), then why would the US side with the merchant?
Very tellling! Imagine if we found ship running guns to IRAN, and the government DEFENDED the merchant!