Unless you personally changed, or paid to have change, all the fluid in the braking system some time in the last 5 years, I would proceed to change the fluid in the system. You realistically have to bleed all the brakes in the order the Bentley manual states anyway (also posted here a million times) BUT you might get really lucky and only have to bleed all three bleeders on each front caliper until they run clean, no bubbles.