Thats exactly what you do need - you'd be wasting your time trying to seal the thing up with silicone. New pan connectors are available from B&Q, Wickes, Plunb Center etc and they aren't expensive. Fitting one though may be awkward, and usually involves moving the complete loo away from the wall so you can get access - it really depends on your individual circumstances. The new pan connectors simply push into the soil pipe, and likewise on the back of the loo.
John, August 2009