Well, check the hoses, they could be expanding, not putting the pressure where it needs to go. Also check pad wear-too much wear, pedal needs to travel farther for same braking.
You can also check and make sure none of the hardware broke, that can cause a bigger issue if a shoe is just flopping around
A leak is still possible- where there is a leak, there is air,air means softer brakes(could be very slow, so fluid may not look like it is receding, especially if it is pulling air back in)