2003 B4000 leaking break fluid

[Buddy's B4000]

Noticed that my truck was down on break fluid today, so i looked under neath the truck to see if i had a leaky line and it appears that that i have a leak inside my left rear break drum, any suggestions on what may be causing the leak or how i may be able to do a quick fix so i dont have to bring it to the shop? Thanks for any help!!

 

[98 ranger xlt]

Wheel cylinder.