2001 Ford E-Series Van engine coolant leaking and appears t

Hello,
Recently noticed spot under my van. Fluid that leaked out appears to be coming from front area of engine(maybe behind belt). This fluid looks kind of brownish and seems more viscious than coolant(maybe oil?). Also, when engine is running, the coolant res. Seems to get lower, but very slowly. Tranny fluid is fine and when I look at oil on dipstick it looks fine as well, but maybe a little low.
What is the problem, how can it be fixed and any estimate on cost to repair?
Thanks!