Both, tried using the standard cyclone into a catch tank to stop oil going into the air filter, but that made the rocker cover leak more. Fitted the Alisport breather and found nothing going into the catch tank, but still had an oil weep from the then new rocker gasket. Now have the new breather piped back into the air filter and it's stopped the rocker leak and doesn't appear to be blowing any oil into the air intake any more. So it seems to have cured mine. As a matter of interest I cut the original cyclone open, and apart from the diaphragm operated non return valve, there's nothing in it at all, any "cyclone" effect would be minimal if anything.