If the brake fluid is low, two further checks to do as the brake fluid will have had to have gone somewhere -
1) check pad wear. They may all be wearing evenly and there's no problem but equally, some pads may be near end of life. Apart from the safety aspect, it's a lot cheaper to replace the pads now than the pads AND scored discs later.
2) check the clutch slave cylinder on top of the gearbox housing. If there's brake fluid there, the slave is about to fail. Better get it replaced while it's still working rather than suffer a breakdown.