Try cleaning the cable terminals up and making sure they are tight then if you have an available second pair of hands, get someone to try and start it and hold the key in the cranking position. While they do this, hit the starter with a hammer(obviously make sure it's out of gear, not too much of an issue if it's jacked up).

If it cranks over after a good smack with a hammer or other suitably weighted instrument, then the starter is sticking.

My advice is to get a new spanking Ford one. I did recently and it cost me about £65 exchange (they need your old unit back) but I get a large discount so add about 25-30% (price becomes around £82-85). It's a new design starter which is smaller so it is not as close to the exhaust. I have not had any more issues with starters since although admittedly it is only 4k miles old....