Ford is not above trying to weasel out of paying claims if they can find a legit reason. I hope they are not trying to do that to you, but you have to try to protect yourself by providing all they ask for to the best you can.

I would be interested in hearing how they think service records relate to a glow plug breaking off.

As far as service records before you bought it, that is tough. Dealers are forbidden by law from giving you any records from a previous owner (privacy concerns). If you bought it from a Ford dealer, they should have documented the condition of the vehicle before they sold it to you. That would be your best case scenario. Worst case would be if you bought it private party with no service records.

I would try running a Carfax report to try and fill in any gaps in service records. Just in case it becomes an issue. Also, register with the Ford owner web site, and then check for service that might have been performed by a Ford dealership.