You give very little info to decisively answer that. How long have you had the bike, when were the calipers last rebuilt? Last brake fluid flush? How is the brake pad wear? even or uneven?
Start with rebuilding the master.
Inspect the rubber line and clamps from the reservoir to the master.
While you're at it, remove the calipers from the mounts, inspect the pistons in the caliper. Any sign of leaking?
Extend the pistons some, clean with brake cleaner or brake fluid, lube the pistons with clean brake fluid and push them back in. When pushing the pistons back in, crack the bleeder valve so the fluid drains into a container instead of back up the brake line into the master.
If you have OEM rubber brake lines, inspect, and consider replacing them. You'll get better feedback with a set of quality steel braided lines and a double bango bolt at the master.
NAPA has a decent selection of crush washers in bags of 10 for like $8.
Hope that helps.