Maybe not so much a leak but the cylinders need replacing. That's what squeaking usually means. My guess is that the clutch isn't being fully disengaged when the car warms up maybe due to a faulty master/slave clutch cylinder and henceforth, hard shifting into first. Also, when I have trouble putting it into first and after I get it in, I let go of the brake and the car feels shaky and wants to move, so it means that the clutch isn't fully disengaged.
& It doesn't look to hard to replace them, just get a good vacuum bleeder to help out after everything's installed. This is my next project to tackle after I fix a few things.