Just noticed from this year's programme:
Shuttle service (free on production of GA ticket) to Arnage and Mulsanne corners will operate from Beausejour roundabout and return to the East Entrance (near Antares tram terminus) and not to the Museum entrance. There's also a shuttle service to and from the Museum Entrance and Beausejour roundabout.
In theory the service is hourly and operates beween 15.00 Saturday and 18.00 Sunday.
I've never used the shuttle service and can't comment on its efficiency