Drivers side rear locks up really easily when I hit the brakes.

Eventually, you will find where the fluid is going, but you don't want it getting slung onto the paint since DOT 3 & 4 is great paint remover. If using DOT 5 (silicone), the high cost will motivate you to find the leak. But, most likely it is leaking onto that rear shoe, as mentioned 10 times. My 1982 Chevy S-10 did that when only 4 yrs old. I found one rear locking up and dragging at a stop sign. Pulled the drum and found the shoe soaked in brake fluid and the wheel cylinder rusty inside. I had never opened the MC reservoir. I imagined lackadaisical union workers at the GM plant let water drip into an open 50 gal drum of brake fluid, or perhaps poured their cokes in there. Now they wonder why their jobs went to Mexico.