if its the gearbox side, its not easy to fit,mine leaked and found it quicker to just disconnect everything from the engine wires/pipes and lift it out and do it, unless u have a ramp and take the gearbox out........

i would recommend buying the gasket carrier aswell as the gasket about 22 quid..

if its the oil pump side, oil pump could be leaking from the block, or the o-ring seal which sits in the oil pump, also the sump gasket around the oil pump area can fail.

hope this helps!