I have a 2002 25 hp merc. ser#0T569650. I noticed a few drops of black oil on the driveway below the lower unit. I checked the oil in the lower unit. It was low and milky but I didn't find any water. The oil in the lower unit was not the same color as on the driveway. I drained it and added new oil and ran it about 30 min. It was full but milky and hasn't leaked any oil. I was told the lower unit would have to be pulled and a seal kit installed. Is this a big project like special tools?