Loosening the head bolts and then re-torquing them to spec's is the 'right' way to do it. However, since the head was recently installed, merely re-torquing them might be OK.
Why not buy yourself a torque wrench and D-I-Y? Then you'll know it was done right. And it'd probably be cheaper than paying a mechanic to do the job (and then you'll have a torque wrench to call your own).
Alfa did issue a TSB about adding a 'stop-leak' additive. If proper re-torquing doesn't help then you could try that.
Why not buy yourself a torque wrench and D-I-Y? Then you'll know it was done right. And it'd probably be cheaper than paying a mechanic to do the job (and then you'll have a torque wrench to call your own).
Alfa did issue a TSB about adding a 'stop-leak' additive. If proper re-torquing doesn't help then you could try that.