Weird brake problem- '85 325e

The brake light came on (1985 325e) so I checked the fluid and it was at the
min mark. I kept adding fluid but it wouldn't come up any higher. I look
inside the car and there is all the fluid in a puddle on the floor mat.
I notice there is somekind of overflow? or pressure relief hose that runs
from the reservoir thru the firewall right into the car. It appears as if
the fluid is running right out of that tube. Is there supposed to be some
kind of check valve in the reservoir to prevent the fluid from running right
out of that tube? Any info on this problem would be greatly appreciated.
I'm hoping maybe I just need to replace the reservoir.
Thanks,
Mike