Metering Unit Oil Type: 
The first type of Metering Unit on the Maserati was an Oil Type. This type used oil from the engine to lubricate the Sleeve and Rotor. On the Metering Unit there is a constant pressure oil pump to increase the engine oil pressure inside the Distribution Unit (see picture). This constant pressure oil pump, operated by a small eccentric on the drive shaft, pumps engine oil to the rotor witch is used for preventing leakage of fuel from the rotor ends and for lubricating the control stop faces.
It is very important that the oil pressure is more than the fuel pressure!! If not, petrol is fed back (with the oil) to the engine with all the resulting consequences.
For all systems, the fuel pressure must not be lower then 7.1 Bar. So, the oil pressure of the oil pump must be higher then the fuel pressure!! Therefore it is very important that the oil pressure of the Metering Unit oil pump be checked every year!! And it should be adjusted on the car by a specialist.                                                       

Metering Unit Oil Less type:
This type of Metering Unit was used on the later Maserati models and has no problems whatsoever after a complete overhaul!! There is no oil pump for lubricating the Rotor Sleeve and the system requires virtually no maintenance.