Oil leak - main seal

[soundguy 13]

I've got an oil leak which appears to be down near the joint between the gearbox and the engine block. Haven't investigated properly yet but its looking like it could be the main seal. If it is, in this thread 

 there is discussion of hockey stick seals. So am I right to think other parts are needed other than the two seals? Can anyone confirm the part numbers please, because I've got 12728 and 32622 as the main seals - what else would I need if this is the reason for the leak?