vauxhall c20xe oil pump

[willzer]

i am trying to source a genuine gm oil pump for a c20xe. the engine is in a escort mk2 rally car the engine has covered 100 stage miles since a full rebuild during our last event the pressure relief valve stuck and it only had 40psi at 8000 rpm after cleaning all was ok until the oil got really hot and the pressure fell back to 40psi again when the engine was rebuilt we used a pattern part oil pump .since speaking to people in the know i have been told to fit a genuine part as some pattern parts are poor quality for competition use. any info will be greatly appreciated regards will philip