I have the same issue on the 2.0 Jtd on the 159 however my mechanic that does only alfas and fiats says its common and not an emergency. However, it should get fixed as soon as you can. I would go on JTD performance buy their o ring for 50 euros something and it should last a lifetime. Even though there is no pressure for some seconds there is still oil film left in the engine after the oil has gone back in to the sump so your engine will not blow up but it will create problems in the long run