It's 50%, and very easily proved to be that way.

There are two possible outcomes.

Outcome #1 someone sits in Mr. Ford's seat before someone sits in the last person's seat. As soon as someone sits in Mr Ford's seat, everyone else can take their assigned seat, including the last person.
Outcome #2 someone sits in the last person's seat before someone sits in Mr. Ford's seat. As soon as someone sits in the last person's seat, you know that the last person cannot sit in their assigned seat.

Because each individual is equally likely to choose the last person's seat as they are to choose Mr. Ford's seat, the answer must be 50%