The small tank is an oil separator, which removes the oil from the crankcase vapours & allows the oil to drain back into the sump. The factory system has the PCV valve on top of the separator, & a hose from the separator to the inlet manifold.
Sounds like your crankcase oily vapour is being put back into the rocker cover.
My RS2000 has the separator, no PCV valve, & a hose that goes from the separator to a catch can.
Cheers