I heard that there are kits for finding leaks in cooling systems. Are there leak finding dye kits for brake fluid? Can brake fluid leak from a clutch slave cylinder into the bell housing? I'm still having a hard time finding my clutch leak. If it's just the connection at the rezivour, (above the master) how could air get to the master without a leak at the master or lower?

Are you losing brake fluid that you can not account for which is causing a problem with your clutch slave cylinder? Or are you just loosing brake fluid that you can not account for?

Traceline may make a fluorescent dye for brake fluid.

I think adding dye to the brake system is a bad move. Brake fluid leaks are readily identified.
There is a chance the clutch slave cylinder is leaking. Pull it out and peel back the boot. If it's leaking you'll see it. The clutch master cylinder can also leak. Check for fluid around the pushrod.

identify your year model and series