They're both right. You need to ascertain the exact source of the leak before tearing anything apart.
Most repair shops have a smoke machine. It injects an
oil based smoke into the crank case. Whereever the smoke comes out, is where the
oil comes out. Many parts stores sell a flourescent dye. Pour it into the crank case and run the engine for a bit. Use a black light to find the leak.
As to your original question, the answer is yes. Older blocks use a two piece seal. This can be changed with moderate hassle with the engine in the car. Newer blocks have a once piece seal. You have to seperate engine and trans to replace it.