About a month ago I had the brake pedal go soft, nothing leaking so I filled the reservoir and it worked fine. Now today the brake pedal has gone soft again, checked brake fluid, no leaking, the only light I have is the traction control.

 

Perhaps the master cylinder is leaking out the rear seal and into the brake booster...?

 

The reservoir didn't appear very low. And since it happened before and started working again I didn't think it was the master cylinder

 

how soft? Soft typically means air in the line. Being a little low wont make it soft unless its really low and you start sucking air. Air will compress when the master cylinder tries to pump uncompressible brake fluid

A bad piston seal in the master cylinder can also make it feel soft as fluid spits around the seal as you apply the brakes