1.7 cdti astravan 2004 - poor starting after a run - gamekeeper

Although when cold my astravan will start ,after a run it will only start after 30-40 secs cranking which cant be good for the starter or battery. I have added a fuel sytem cleaner and changed the crank sensor to no avail. Its as if it needs to self bleed but not to bad on initial start up. any thoughts.. thank Big Kev