After chasing a brake leak for a week, it turned out to be the piston inside the drum.

Tip for adjusting the drums.

LEFTSIDE
Expand / Tighten = Clockwise
Contract / Loosen = Anti Clockwise

RIGHTSIDE
Expand / Tighten = Anti Clockwise
Contract / Loosen = Clockwise

Leaking brake piston.

New brake piston $38.

Probably should've changed them both but the other one seemed alright.