Rolls-Royce Phantom II in the workshop

The Phantom II I look after has come back for a couple of jobs. I'm going to fit a new cork seal into the fuel tap that site under the Autovac and have removed, cleaned and polished the needle in the float chamber. I've also removed & inspected the distributor cap & adjusted the points. I'm trying to find out why it starts to run badly after an hour's drive but, once it's cooled down a bit, runs fine. It also has a tendency to leak fuel from the overflow after a run. Fuel pipes and filter have also been removed and checked for cleanliness.