1991 3.0 Mighty Max 4x4 Truck Norris Edition

So I am moving as fast as I can to get this truck back on the road

It has a brake leak - it looks to be behind the brake fluid reservior

What is that round part? What do you think that I need to replace?

I can get a below pic if needed



Leak.jpg10176000_10152291581172192_1616914199_n.jpg