1986 190D - mysterious brake fluid leak

[PKdavidson]

I've noticed my brake fluid level has been slowly dropping over the past couple of weeks. It's been into the shop and no one could locate the culprit. However this morning while driving to work my foot slipped off the clutch pedal. I noticed that there's a tiny bit of clear fluid on the arm of the clutch pedal itself. The brakes also hiss every time I press the brake pedal down. Guessing my master cylinder seals are giving up? Or could it be my clutch slave?

Here's some extra info that may or not be relevant:

The previous owner was having some caliper sticking issues in the rear, went ahead and rebuilt the rear calipers - still had a sticking issue. He went through a couple of brake master cylinders and then eventually decided to change the brake connecting rod length from the brake booster. So my pedal is a little lower than it should be. It's not supposed to be adjustable but the friendly eastern-european previous owner found a way. I never noticed the sticking issue until later when it was cold in GA (in the 20s) and I noticed my parking brake was stuck. I've since replaced the completely-worn parking brake shoes and this problem has disappeared. I believe the PO missed this problem and screwed up the new master cylinder in the process.