Stuart,

Your advice is sound be it doesn't jive with what the customer reported.
If the injector is leaking it should start rough on at least 3 cylinders
but it starts OK..........I think the fuel pressure should be checked
(along with your suggestion) and also check the O2 sensor function.
Additionally the fact that the coolant temp sensor has been "replaced"
doesn't mean it functioning correctly..........

Regards,      JP