The main advantage of the AS355F2 is an increase in the MTOW from 2400 to 2540 kgs, though the increased weight is only permitted for performance class 2 operations. In association with this there is a hydraulic damper fitted to the tail rotor control system to assist with control of the tail rotor in the event of failure of the right hand hydraulic system below the Vtoss of 40 knots.
Never had a problem with oil leaks or Nr stability. I also never had any problems with icing. The weak point of all the AS355 series is the electrical system, especially in a damp climate. After heavy rain the fire warnings quite often illuminate until such time as the engines have been running for a bit and the system dries out. There is also a problem with moisture getting into the double electrical emergency cut-off switch which can stop you from being able to start up if you shut down in the field and has caused some rather unusual failures in flight, depending on which electrical system you have fitted (and there seem to be a lot of different electrical systems on 355s). Also if, when flying in heavy rain, you leave the forward air vent open, rainwater gets in through it, shorts out the circuit board for the RPM warning system and the horn will come on, causing great alarm until you realise that the Nr are still steady!
Overall though, despite being a bit long in the tooth now, a fine machine with reasonable performance.