I was looking at the rear drum brakes on my 89-5.0 Mustang.

I decided to check the wheel cylinders to see if the pistons were not sticking.
A mechanic once told me to push the pistons back in with a screwdriver to see if they are free and if they go back in they are ok.

Tried the drivers side and both pistons went back in,then the rear piston started leaking some brake fluid,not a lot but enough to make some drops on the ground.
I cleaned the brake fluid off with brake cleaner,put the drum back on and pumped the brakes to get the pistons back where they were and it hasn't leaked a drop with the brake pedal under pressure.

No signs of any leakage before doing this and the master cylinder is right up.I didn't try it on the passenger side after this happened,lol.
Wheel cylinders are original and never showed any signs of leakage.

Any recommendations or cause for concern or did I just maybe push the piston in to far on the rear piston?